So, your love of truth is subordinate to your need to believe something.

How can you think of finding truth if there are things that you exclude from discussion?

It’s like saying: I’ve lost my keys, let’s look everywhere to find them, but, please, don’t look in that room. What if the keys are precisely in that room? — Angelo

It's not that the skepticism regarding the principle of non-contradiction (PNC) is excluded from the discussion, I don't think. I'm not saying we should cover our ears and sing 'la la la' if anyone ever calls PNC into doubt, or shush them and tell them that they can't ask those questions if they want to be in the philosophers' club. Rather, I'm saying that, after reflection, it becomes evident (at least I and many philosophers think so) that PNC is absurd to doubt. In his Metaphysics, Aristotle wrote a whole chapter, I think at least three pages, where he examined many of the absurd consequences that would follow if PNC were denied. So you should question PNC, and then, after seeing the absurd consequences of questioning it, accept PNC as a fundamental axiom of all rational thought. You can also question reductio ad absurdum as a method of proof, and I think you'll see that, if absurd propositions are worthy of rational assent, then human reason cannot distinguish between what is and what is not worthy of rational assent, in which case reason is a useless tool and we might as well stop using it.

Also, I think love of truth necessitates belief, in the same way as love of color necessitates vision. You can't love something to which your mind has no access. Truth and falsehood are attributes of propositions, and propositions represent beliefs. We can state propositions without believing them, but that is either lying, in which case we try to make others think we believe things which we do not actually believe, or some kind of game playing, like when we tell jokes or make up stories. But jokes and made up stories only make sense in the context of belief. Both of them rely on and mimic belief insofar as in telling and hearing jokes and stories, we consider something we do not believe, like an amusing scenario or a fantasy world, as if we actually believed it were true.

If we want to make use of a real radical consideration of subjectivity, each of us must consider his own subjectivity in the “here and now” of the moment when he is thinking. This is the true consideration of subjectivity, that is able to demolish any idea of truth, be it universal or not. If I take into consideration my subjectivity here and now, I realize immediately that I have no way to give any kind of guarantee about what I am thinking of, what I am talking about. — Angelo

Could there perhaps be confusion between psychological and epistemological certainty? Psychological certainty is how confidently I believe something. Epistemological certainty is how justified I am in believing it. Both pertain to the subject who believes, as opposed to the object of belief. Now psychologically, I feel quite confident about many things. But then, when philosophical thought puzzles are posed, my confidence may be more or less undermined, depending on how I react to pondering them. But I can be well justified in believing something even if my psychological feeling of certainty is very low, and I can be very poorly justified in believing something even if my psychological feeling of certainty is very high.

So what constitutes a good enough justification for a belief that one can be epistemologically certain that it is true? I would say I can be epistemologically certain of a belief if it follows logically from other beliefs of which I am epistemologically certain. But if I don't have foundational beliefs of which I am epistemologically certain, an infinite regress would ensue. So I would say that a belief is foundational if it is indispensable. And a belief is indispensable if it cannot be denied without undermining all my other beliefs. For instance, the belief in the principle of non-contradiction is indispensable because, if I deny it, then all my other beliefs may be true and false at the same time, in which case I can't really believe anything.

I would say that the belief that your knowledge extends beyond the here and now is indispensable. Yes, if all you knew were the here and now, you could not guarantee anything. For knowledge requires justification, and justification requires thought, and thought requires time. If I think something is true at this moment, then I must have justified it at some point in the past, otherwise I'd have no reason to believe it true. But if I only knew the here and now, I'd have no way of knowing whether I'd justified any of my beliefs in the past, in which case I'd have no reason to believe any of my beliefs were true. So memory must be at least somewhat reliable. For if memory were totally unreliable, then I'd have no way of knowing anything.

Objective reasonings give us the illusion of being working, just because we forget ourselves in the moment we describe them.
This might be used as an argument against my conclusion about the contradiction I showed in my preceding message: since I can’t guarantee the correcteness of what I said, I can’t be sure that what I described was really a contradiction. But this makes me think that other people must be in the same condition: how can they guarantee that their reasoning is free from errors? How can they be less uncertain than me? — Angelo

I think you may be sneaking a pinch of naive skepticism into your argument. Because you're claiming to believe two things 1) I am in this condition where certainty is impossible, and 2) since I am in this condition, others probably are as well. Either you're claiming 1 and 2 to be true or at least probable propositions, in which case you are guilty, I think, of naive skepticism. Or, you are just attempting to express your subjective experience of considering philosophical ideas, and you are not stating propositions which you believe are worthy of rational assent. What else could you be doing?

What is important now is that I ended up in questions, not in statements. Who will be able to put a stop to our questioning, our doubting?
Relativism and scepticism can be attacked if they are considered as sources of statements: “nothing is absolute”, “nothing can be known”. But I think that their real nature is questioning, doubting, without giving nor suggesting any answer. — Angelo

This sounds more like a spiritual practice than a philosophical position. In fact, I've heard that ancient skepticism, along with other ancient schools of philosophy, was a spiritual practice. As a skeptic, you refuse to give assent to any propositions, and instead you question and doubt everything proposed to you. Rather than seek out things to believe, you seek out reasons to undermine belief, and your goal is to believe as little as you can, ideally nothing. Or, perhaps that's not the main goal of your life, but it is your goal when you philosophize. Either way, I would call that kind of skepticism a spiritual practice, not a philosophical position, because it describes a way of life as opposed to a set of propositions to believe. Skepticism may be your way of life, or, more likely, it is not your way of life, but only the way you like to do philosophy. You may even selectively apply skepticism to some philosophical problems but not to others. For instance, you may be a skeptic when discussing metaphysics but a rigid dogmatist when discussing politics (I suspect that a lot of people on this site are like that, although perhaps you aren't).

If you have chosen to pursue skepticism as a way of life, I doubt I can convince you to stop by means of philosophical argumentation, because the whole point of skepticism is to undermine philosophical arguments. In fact, there's nothing really incoherent about believing nothing, although I suspect that most people who call themselves skeptics do believe in some things. But I think that the mission of skepticism is diametrically opposed to the mission of traditional philosophy. Philosophy, traditionally conceived, is love of wisdom, and wisdom, traditionally conceived, involves knowledge, especially knowledge of important truths that are fundamental to understanding reality and human life. Philosophy pursues knowledge of these truths by means of rational argumentation, and it argues by means of propositions that can be either affirmed and believed or denied and disbelieved. Since the style of skepticism you are proposing seems to replace affirmation and denial with perpetual doubt and propositions with endless questions, I think it falls outside the realm of philosophy. You can engage with a philosopher as a skeptic, but your mission as a skeptic is not the same as the philosopher's mission. He seeks truth, you do not. He uses argumentation to discover what ought to be believed, you use argumentation undermine all beliefs.

1) At the beginning they trust memory and logic;
2) they just apply logic
3) and they discover that the application of logic demolishes trust in memory and, as a consequence, in logic as well;
4) then they become skeptic.

What is demolished by the application of logic is the initial trust on memory and logic, because this initial trust is the necessary base that makes possible the conclusion. — Angelo

If memory skepticism really could be demonstrated from undeniable premises, then I suppose I'd have to assent to it, and, as a result, fall into radical skepticism. But once a radical skeptic, I'd have no reason to remain as such or not to remain as such. However, I think you're right that, if it is logically demonstrable that memory cannot be trusted, and human logic (by human logic, I just mean the ability of humans to use logic and trust that it leads to truth) depends on memory, then it is demonstrable that human logic cannot be trusted. And if it is demonstrable that human logic cannot be trusted, then it is unreasonable to believe in anything. Human logic would then be like a defective machine that conked out every time you tried to use it. It's not that 'belief in logic is unreasonable' would be a reasonable proposition. Rather, the very attempt to construct reasonable propositions would lead to self-contradiction and absurdity. Does this sound right? Is that what you're saying?

That's all true, assuming memory skepticism is demonstrable. But I don't think it is. I think it's perfectly reasonable to think it self-evident that memory is generally trust-worthy. Or, if I were, for instance, suffering from alzheimer's, and my memory was impaired, I would know my memory was impaired. But it may be self-evident that I was not, for instance, created one moment ago. That seems fairly self-evident to most non-philosophers. And even if you doubt it, I don't think you can prove that it's not self-evident. And since all our beliefs rely on memory, I can perhaps assert truly 'either memory is self-evidently at least somewhat trustworthy, or human knowledge is impossible'.

I think that you reach the conclusion that skepticism is self-refuting because you consider the question as everything happening in the same instant, like in a photo, while instead it is a sequence of reasoning steps that happen over time, by stages, like a film. — Angelo

I think your argument works insofar as it shows that, if having beliefs entails contradiction, it is unreasonable to believe anything. But then, once the conclusion is accepted, it must also be rejected, since if I believe that's it's unreasonable to believe anything, then this belief is also unreasonable. If reason is like the machine that conks out when you try to use it, you just have to stop using it. If you're computer conks out when you turn it on, you can't use your computer to look up what's wrong with your computer. In the same way, if logic refutes itself, you can't use logic to prove that one should be a skeptic. All you can do is observe logic refuting itself. So, to use your film analogy, you can observe logic undermining itself during the part of the film when logic is still in use. But then once you advance to the part of the film when logic has already been undermined, you can no longer use it to show that logic undermines itself. Yes, the argument unfolds in time, but no, you, as a temporal being, cannot step outside the time in which the argument unfolds and simultaneously assert both the premises the conclusion. Once reach the conclusion, all you have left of the premises is your subjective reaction to having watched logic undermine itself. You can't continue to assert the premises once you've accepted their conclusion, which undermines all premises. You don't have a logical argument to justify your disbelief in logic. You could rewind to the part where logic undermined itself and watch it again. But once it happens, you have to go back to believing nothing. I think Wittganstein puts this well when he says (roughly) that once you climb the ladder and stand on the higher, philosophical ground, you have to kick away the latter.

So, back to the proposition 'either memory is self-evidently at least somewhat trustworthy, or human knowledge is impossible': you cannot reasonable maintain that human knowledge is impossible. However, I see no reason why you can't reasonably maintain that memory is self-evidently at least somewhat trustworthy.

Here's one other possible argument against memory skepticism: change seems to be perceived, and one cannot perceive change without perceiving multiple instances of time. But if one perceives multiple instances of time, one must experience both past and present, because the present constitutes only a single moment, and the future cannot be perceived. And the perception of the past is memory. So it is self-evident that we have memory at least of the previous moment. But in the previous moment, we also remembered the moment before that. So we can at least remember the previous two moments. This argument cannot be infinitely repeated, for the further we recollect back in time, the more vague our memories become. Maybe the argument only works to prove that I remember the previous 10 seconds. Perhaps it doesn't work at all. I haven't thought about it much. But I suspect that other arguments against memory skepticism could also be formulated.

I think that reflection is extremely important, because many people don't really question assumptions. I am sure that many of the philosophers were extremely reflective. However, I have found more on the topic of reflection in books outside of philosophy, such as ones on critical thinking. Also, I am familiar with an author, Gillian Bolton, who looks at reflective writing as a practice. However, I think that you are correct to point to the importance of reflection on ideas, and I see this as an essential aspect of philosophy. — Jack Cummins

Yes, I agree that reflection should question assumptions. But since, as I also argue, some beliefs are foundational, reflection should also reveal that some assumptions are necessary. Because without any foundational assumptions, we would have no premises from which to derive conclusions, and reflective knowledge would be impossible.

Each of the nodes of the truss are connected to at least two other nodes. A load placed on any node is transmitted along the truss members to other nodes and throughout the rest of the truss. I see this as a metaphor for knowledge. I can't add a new node anywhere I want. The rest of the nodes are significantly constrained in their movement by the interconnected members of the truss. If I want to make any major changes in the network, especially something that isn't consistent with its current design, it will take a lot of effort throughout the network, not just in the location of interest. — T Clark

I like the node/bridge analogy, but I think I can expand upon it to defend my point. In order for a structure to function, it needs to rest on solid ground (unless it's something like a satellite). Solid ground works as an analogy for foundational knowledge. There are some things we know independently of reflection or demonstration, like the content of our perceptions. In order to construct a system of beliefs that corresponds to reality, we must built upon the ground that sensory experience provides. Moreover, if our structure is going to stand, we need to take account of the principles of mechanics that govern the physical world and also the gravitational force exerted by the earth. These work as an analogy for the foundational principles of logic and mathematics, and maybe even a few metaphysical principles like the principle of sufficient reason. Thus, we must build our belief systems upon the ground of perception, our material foundation, and in accordance with basic principles of reality (like logic), our formal foundation.

An analogy for pure coherentism might be building something in remote outer space, where there are no external forces. There, any structure would hold to together and stay in place, and thus, in order to change the structure, you'd only need to account for the structure you yourself had laid. If a belief system were purely coherentist, the only means to determine the soundness of a belief would be to compare it with other beliefs. No foundational beliefs would exist to base the system upon. An analogy for pure foundationalism might be something like laying a path on the ground. There, the structure would not extend any higher than the ground on which you founded it. Analogously, a purely foundational belief system would not demonstrate conclusions from premises or reflect on the interconnections between different items of knowledge. The only object of belief within such a system would be immediate perceptions. I think most animals probably operate according to a purely foundation belief system. A dog, for instance, believes, at least in a sense, that his master is home, or that he smells a rabbit. But the dog only believes these things because his perceptions immediately and unreflectively engender these beliefs in him. A human on the other hand, can start from foundational beliefs and build complex intellectual structures upon them, like scientific theories and historical narratives.

That's true, Descartes idea was similar. After reflecting on his beliefs, he claimed to discover that cogito ergo sum was the only one he couldn't doubt. But I think his argument differed because cogito ergo sum wasn't really his foundation. He demonstrated the cogito from these premises: 1) if I do not exist, then I am deceived, 2) if I am deceived, then I exist. Thus, his foundation must have included the two premises, sufficient notions of selfhood, deception, and existence for the premises to be intelligible, and the principles of logic, which enable the proposition 'I exist' to be derived from the two premises. However, Descartes did not explicitly state that these were his foundations, and he seemed to imply that the cogito was his foundation. And he also didn't distinguish his reflective knowledge of the cogito, which he acquired through examining his beliefs, from his foundational knowledge of it, whereby he would immediately know his own existence independently of demonstration. He even seemed to imply, by his method of argumentation, that he arrived at knowledge of his own existence through reflection and demonstration. If all our knowledge depends on reflection and demonstration, then it's all coherentist, so Descartes seemed to imply that all knowledge is coherentist. The cogito was not foundational for him in that it could be known without reflection, but rather in that, upon reflection, it was the only belief that proved impossible to doubt.

I'm not familiar with Sartre's idea, but it sounds worth investigating.

Well, I'm a Humean when it comes to the possibly universal truth of you having woken at 8am today. You might be totally mistaken. You might not even be there though I think it is pretty likely that both things are sensibly true, you probably really did wake at 8am and you really most probably do exist. — hwyl

By a Humean, do you mean a memory skeptic? I didn't know Hume was a memory skeptic, but I suppose it makes sense that he would be.

Here's an attempted rebuttal of memory skepticism. If memory skepticism is reasonable, then it is reasonable to think that we can't differentiate between knowledge in the memory and mental fabrication. But if we couldn't differentiate between knowledge in the memory and mental fabrication, then we couldn't make any reliable judgments. For rational judgments move from premises to conclusions, and we can only be justified in our conclusions if we remember their premises. We can be skeptical regarding individual memories, but if we suspect that our memory is generally unreliable, then this comprises our ability to justify any of our beliefs. Thus, whoever is skeptical of his memories is epistemically compromised i.e. he cannot be justified in any of his beliefs. If I am not justified in believing my memories, I am not justified in believing that I remember premises, so I am not justified in believing the conclusions I draw, in which case no judgment I form is justified. But this is self-refuting, since if no judgment I form is justified, my judgment that memory skepticism is reasonable is unjustified.

I think the best competitors for being universally true are logical propositions. But then again I just might imagine that a logical proposition is sound, as it is just my limited brain that tells me that it is universally true. It's not really within the realm of reasonable suspicion but it is within the realm of suspicion. — hwyl

If it's not within the realm of reasonable suspicion, then wouldn't it be within the realm of unreasonable suspicion? And if the suspicion is unreasonable, I think it should be discarded. Isn't one of philosophy's main functions to differentiate reasonable from unreasonable ideas, so the latter can be discarded.

Thanks for the thoughts. I'll just say someone who's mind is in constant flux cannot communicate his experience to someone who believes in absolute Truth — Gregory

I suppose I can't argue with your private experiences. But I doubt your experience is that much different than mine. We are both humans, after all. Our DNA is what, like 99.6% the same?

I can't think of anything I can hold on to, consider, and judge to be certain. — Gregory

In his metaphysics, Aristotle includes a chapter showing how, if you deny the principle of non-contradiction, you are lead into absurdities. His arguments are somewhat complex, but I think the overall point is fairly self-evident. If a thing can both be and not be in the same respect, then this sentence might be both true and false in the same respect, in which case it both means nothing, or it means both something and nothing at the same time. Or, consider a married bachelor. A bachelor is an unmarried man. So if a bachelor is married, he is not a bachelor. So when you say, 'unmarried bachelors exist', you are just speaking nonsense.

Life moves too fast, at least for me. — Gregory

I suppose you're right that even the thought process necessary to arrive at the principle of non-contradiction takes time. And it's conceivable that in the time required to demonstrate the absurdity of contradictions, I was deceived by a Cartesian demon, or something. I think one can respond to the notion of a Cartesian by becoming a radical skeptic. But that's not really reasonable, since a Cartesian demon may not be possible, and the only way to determine whether or not it's possible is to use reason. Even if I can't prove beyond a shadow of a doubt that no demon exists, this isn't reason to become radically skeptical. Because if radical skepticism is true, then there's no reason to be a skeptic. But if radical skepticism is false, there are probably good reasons to deny Cartesian demons, even if I haven't totally figured them out yet. And without the demon, it becomes possible to believe in self-evident things, like non-contradiction and the reality of perception. And from these self-evident things, it is at least plausible that one might be able to construct a well reasoned philosophy.

too much philosophy likes to break down instead of building up. — Gregory

It is true that philosophers often prefer to break down reality than build it up. But these are the successors of the sophists, whom Plato and Socrates opposed. Plato's notion of a true philosopher, a lover of wisdom, is opposed to the notion of a sophist, a person who uses clever thought experiments to sow seeds of doubt. Sophists are useful to motivate philosophers to develop better arguments, but the quest of the philosopher, to build up knowledge and understand reality, is fundamentally opposed to the quest of the sophist, to tear down knowledge and distort reality.

The Catholic Church has defined that judgment comes right after death and that you don't wait to go to heaven. In my understanding though, the general judgment and the private judgment are the same and the soul never is nor can be without the body. So there is no afterlife like atheists say OR there is no death (the dead body being a shadow of your new body in paradise) — Gregory

I think that was the opinion of Pope John XXII, but the Church later condemned it. According to Aquinas, the soul is the form of the body. So a plant has a soul, but the only function of its soul is to animate it, causing it to grow, self-sustain, and reproduce. So the plant soul disappears with its death. An animal soul has an immaterial effect, in that it gives rise to consciousness. But irrational animals are only conscious of their sensations, and once their bodies die and cease to supply sensations, their consciousness vanishes and along with it, their souls.

Now unlike irrational animals, humans can understand abstract concepts. Abstract concepts cannot be understood using material organs. This is evident 1) because abstract concepts are universal, whereas all material inputs are particular. An abstract concept can represent infinite entities, such as 'all triangles', whereas sensations only represent single entities. 2) abstract concepts supply knowledge of the forms of things. Thus, to know something is to possess its form. But if a material thing possesses a form, it becomes a material instance of it. For instance, if a body possesses the form of a tree, it is a tree. But the intellect can know the essence of a tree without turning into a physical tree. Thus, the intellect is an immaterial reality that can contain the forms of material things. 3) Abstract concepts are the objects of reason. But if abstract concepts were understood using a material organ, then our reasoning regarding them could be made to contradict itself by a material change. To illustrate, something sweet can be made to taste sour by a material change in the tongue. But if reason depended on a material structure and would be different with a different material structure, then reason does not reflect reality but only the structure of our brains. But this notion leads directly to radical skepticism which, I and others (like Aristotle) have argued, is self-refuting. 4) if the mind is purely material, then my decisions are determined by material inputs, and this seems to run contrary to my extremely fundamental intuition that I am a rational agent who is free to choose from multiple options, not determined by mechanistic or random material processes.

Now granted that abstract concepts are not understood using a material organ, they must be understood by an immaterial faculty, namely, the intellect. And based on our immaterial, intellectual knowledge of things, we have the power to make decisions which are not determined by material forces. So along with our immaterial intellects, we have immaterial wills. These two powers constitute our immaterial souls. Now the human soul is partly material, since it is the form of the body, but it is also partly immaterial, since it gives us the power of intellect and will.

Since the things we know with our intellect come from sensation, our knowledge from birth until death is confined to sensible realities. But once the body dies, and the immaterial soul is separated from it, it will retain its existence even without sensation. For, as Plato argues in the Republic, an immaterial thing has no principle of corruption. Whereas a body, which is composed of parts, can be taken apart and thereby destroyed, the soul, which is a simple, immaterial form, cannot be taken apart in this way, so it cannot destroyed, at least not by natural causes.

And just as the immaterial soul has no natural principle of corruption, neither does the knowledge it contains. So we will retain our abstract concepts and our judgments regarding them after death. However, the human intellect is designed to understand abstract concepts with the help of the material imagination. When we consider the concept of a triangle, for instance, our understanding is aided by mental pictures derived from sensation. So the soul separated from the body is incomplete. Its knowledge is vague without images, and has no source of new knowledge.

Without its body, the separated soul is impotent and unhappy. However, God can supply the separated soul with a vision of the divine essence. If the separated soul loves God, this vision of God will make it supremely happy, since it will be united to an infinite and perfect reality that it loves. But if the separated soul does not love God, the vision of God will only cause it to experience suffering. For to suffer is to have your will denied. And if you do not love God, you will things that are contrary to God's will. And a vision of God is a vision of Gods all powerful and irresistible will. So if you will what is contrary to God's will, and you have a vision of God, one will see with perfect clarity that your will is denied, and that you can never possibly have any hope of ever having your will satisfied. Thus, for those who love God, the vision of God is supremely joyful. But for those who do not love God, the vision of God is supremely painful.

Obviously, this is a lot of material, and I haven't adequately justified any of it. But I hope it sheds some light regarding how one, like Aquinas, can believe in life after death separated from the body.

This is why I don't think relativism refutes itself. Someone can think everything is relative and hold that belief on probable grounds, and that on probable grounds, to infinity and we don't understand infinity. Our bodies and everything is flux and we can't understand it. We are born to have faith, give mercy, and hope — Gregory

Maybe I agree with you in the sense that, in order to believe that natural human reason can lead us to truth, we need to take a kind of leap of faith. If we deny that human reason can lead to truth, then we won't respond to reason based arguments to the contrary. So radical skepticism is an unfalsifiable position that requires a kind of faith in reason to overcome. And maybe this faith in reason is also tied up, in a complex way, with hope and mercy and the other virtues that perfect human nature.

I don't totally agree with you. I see no complete certainty in intellectual matters for us on earth. At the back of my mind I suspect it is all just matter that we know and think with. If I could prove spirituality it would be based on faith no more, right? — Gregory

That depends on what you mean by certainty. If by certainty you mean the impossibility of self-doubt, then I agree that that is impossible for a human to have. But doubt can sometimes be more of a psychological than an epistemological state. I have no epistemic reason to doubt that my plane will almost certainly arrive safely at its destination, for instance, but I still might experience fearful doubt psychologically. But if by certainty you mean adequate justification to constitute a genuine item of knowledge, then I disagree. For instance, I believe we have adequate justification to know that 1+1=2. And while we might doubt this in psychological way, or come up with a wild thought experiment that causes us to question this knowledge, I don't think either of these are sufficient to undermine our knowledge that 1+1=2.

I also don't think you need faith to believe in spiritual realities. I think the hard problem of consciousness provides adequate reason to believe that sentient beings are not purely material. Perhaps you can argue that I'm wrong about this, but I think it's at least theoretically plausible that sufficient evidence exists to justify belief in spiritual realities.

Yes. Ideas are always in flux but we go with the best probabilities as they present themselves to our souls — Gregory

It seems to me that knowledge of probability presupposes knowledge of certainty. For instance, if I have probabilistic knowledge that I probably won't roll snake eyes in dice, this is because I have certain knowledge regarding the nature of dice rolling. To illustrate this in a more technical way. Suppose I can only know something with at most 90% certainty. Then, if I know something with 90% certainty, I can be at most 90% certain that I know it with 90% certainty. So I only know it with 81% certainty. But in that case, I can only be 90% certain that I know it with 81% certainty. Do you see that pattern? The probability of any item of knowledge will just be repeatedly multiplied by 90% at most and approach 0. So it seems that if I know something with 90% certainty, I must be certain about something that guarantees my ability to reliably estimate probabilities.

Aquinas says in Contra Gentile that stars, the moon, and the sun are unquantitative. He had very esoteric opinions on "heavenly bodies" as if they were Platonic Ideas instead of real matter. That's one of the reasons Galileo got in trouble when he used his telescope. People claim the telescopes were faulty, had dirt in them, or were instruments possessed by the devil — Gregory

Aquinas' ideas about the heavenly bodies came from Aristotle mostly. Ptolemy used Aristotle's theories to create a very reliable geo-centric system for measuring time. His ideas were used to develop the Gregorian calendar, and Medieval Christendom relied upon the Gregorian calendar for many things, both religious and secular. So it makes sense that people believed this stuff, since it worked well for their practical purposes. Although I admit that they might have been excessively harsh towards Galileo.

So for Aquinas substance comes out of matter by form and the appearance of substance is accidents? Then wouldn't essence, nature, and quiddity be just another word for the matter\form composition? There is another old Greek word used in this question to but I forget it — Gregory

Yes, in the case or bodily substances, essence, nature and quiddity all refer to matter/form composition. But Aquinas also believes in immaterial substances like angels and God. Angels are pure forms, and God is pure actuality, or infinite existence. I don't know the Greek word. Is it it ousia or hypostasis?

I don't think we can know anything for sure and on this Kant's position seems most accurate. But Hegel started with Kant but added Aristotle's and Aquinas's ideas as phenomenologically relevant to understanding Kant's. We can't stay in a world where we know nothing and Aquinas is a good start in believing again in knowledge — Gregory

It seems like you are both saying that we can't know anything for sure and that we can't not believe in knowledge. So we can't know anything, but we must believe that we can know things? Are you making a distinction between different kinds of knowledge?

This sounds closer to redundancy theories in my mind. Although, there is significant overlap between coherentism and redundancy theories. Yes? — Shawn

By redundancy theory, do you mean the idea that prefacing a statement with the phrase "it is true that" doesn't add any intelligible content to the statement? I agree with that. But how does that relate to what I wrote.

See Susan Haack's
foundherentism. — 180 Proof

That sounds like it agrees with what I wrote. But it doesn't sound like she makes a similar distinction between unreflective knowledge, which is prior and justified according to foundationalism, and reflective knowledge, which is subsequent and justified according to coherentism. Or, in other words, the distinction between knowing something at the level of foundationalism, and knowing that one knows something at the level of coherentism.

Kant said however that we can know phenomena as it presents or appears to us. The noumena is what is unknowable and Aquinas says somewhere that we can't fully understand things without thinking with the mind of God. So maybe they agree. — Gregory

I think Aquinas holds that we can't know the essence of a substances directly, but we can only know it by means of its accidents. So, for instances, bodily substances have magnitude in three dimensions, and they can be moved from one place to another, and they can be divided into parts. From these accidents, I form a notion of bodily substance. Now for Aquinas, we have direct knowledge of the accidents that impact our senses, and these accidents really reveal the essences of the substance in which they inhere. Accidents only have essence insofar as they inhere in a substance, and thus the essence of a sensible accident is just a particular manifestation of the essence of the substance in which it inheres. Moreover, accidents are caused by the substances in which they inhere, and in this case, the effect points directly to its cause. So, for Aquinas, we do know the essences of bodily substances, but in an indirect and incomplete way, since we only know them through the accidents that impact our senses. Only God (and perhaps the angels to an extent) can have full and comprehensive knowledge of the essences of things.

For Kant, the distinction between substance an accident is a mental construction. All the things that Aquinas considers sensible accidents really inhering in bodily substances, Kant considers mental representations with no necessary correspondence to things in themselves. For instance, Aquinas believes that bodily substances actually have spatial dimensions, like length and width, but Kant believes that spatial dimensions are just forms we impose on our intuitions. Aquinas believes that substances actually have causal powers, like fire's power to heat, but Kant believes causality is just a mental construct whereby we organize our perceptions.

I think Kant borrows many of his categories from Aquinas and Aristotle, but he conceives them in a fundamentally different way. Aquinas is a realist, Kant is an idealist.

Kant holds that senses are more known by intellect than intelligible objects are know by us. This leads him to discount all Aquinas's arguments for God and I agree with that. — Gregory

I think Kant's argument against the Thomistic proofs of God is that the categories we use to understand the world like subtance/accident, cause/effect, one/many, are just mental constructs whose purpose is to organize sensory information. They don't actually represent the natures of things as they exist in themselves. So these categories can be used to describe objects of possible experience, like stars or molecules. Because these things are sensible, at least in principle. But since God is not sensible even in principle, the categories of thought do not apply to Him. Kant acknowledges that our category of causation points toward a First Mover who wisely creates and orders the cosmos. But since this First Mover cannot be a sensible being, His existence cannot be affirmed, for existence itself is just a category whose legitimate employment is restricted to the sensible realm.

Now I think Russel's critique of Kant is basically right. He says, roughly, that Kant's theory relies on the assumption that the mind really exists and orders its sensible intuitions according to the forms of sensibility and the categories of the understanding. But if the mind exists and employs these artificial categories, nothing prevents the categories from being changed, so that 2+2 might equal 5. Also, if the structure of the mind exists, it either exists as a noumenom or phenomenom. If it exists as a noumenon, then Kant has contradicted himself and affirmed things about noumena. If it is a phenomenon, then the the structure of the mind for which Kant argues in the First Critique is a mere appearance, in which case the mind may not actually work the way it appears to work. And if we don't know how the mind actually works, we cannot legitimately refer to its structure to justify our beliefs. For the categories that appear to us may not be the actual categories, and the principles of logic our thought appears to obey may not be the actual principles it obeys.

The problem of the concept of universal truth is that it contradicts itself: if a truth is universal, it must be able to face any consideration and, particularly, the consideration that we humans are unable to think without using our brain. This means that we are unable to think of the concept of universal truth without using our brain. Since any concept of universal truth is necessarily dependent on our brain, it cannot be universal, because our brain doesn’t seem so universal. The interesting thing is that this conclusion comes exactly from the premise that some universal truth exists. So, assuming that universal truths exists, brings us to the conclusion that universal truths do not exist. If universal truths exist, then they don’t exist. That’s the contradiction. — Angelo

Let me try to restate your argument.

Show that no proposition is universally true:
1. For all propositions P, if P is universally true, it is necessarily true for all thinkers. (premise)
2. For all propositions P and all thinkers x, if x thinks P, and x is human, x thinks P by means of a brain. (premise)
3. For all propositions P and all thinkers x and y, if x thinks P by means of brain and y thinks P by some other means than brain, it is possible that the truth-value of P for y will be the opposite of the truth value of P for x. (premise)
4. For all propositions P, it is possible that there is some thinker, y, who thinks P by some other means than a brain. (premise)
5. For all propositions P and all known thinkers x, if x thinks P, then x is human. (premise)
6. Suppose that some known thinker, b, thinks some proposition, Q.
7. B is human (5, 6, ui, mp)
8. B thinks Q by means of a brain (2, 7, ui, mp)
9. Possibly, some thinker, c, thinks Q by some other means than a brain. (4, ei)
10. Possibly Q has a truth-value for c, and possibly it is the opposite of Q's truth value for b. (3, 8, 9, ui, conj, mp)
11. Possibly, Q has opposite truth values for b and c. (10, simp)
12. If Q is universally true, it is necessarily true for all thinkers. (1, ui)
13. Q is not necessarily true for all thinkers (11, def.)
14. Q is not universally true (12, 13, mt)
15. For all propositions P, P is not universally true (14, ug)

Does this represent your argument well? Perhaps it is unnecessarily complex.

I think the problem is in premise 3. Now when I say, for instance, that P is true for x and false for y, this doesn't mean that x and y just have different opinions. I means that x is epistemically justified in believing P, and y is epistemically justified in denying P. Now this strikes me as impossible. For, Gettier cases aside, if someone is epistemically justified in assenting to a proposition, then the proposition is true. If this were not the case, then there would be there would be no criteria to distinguish certain from uncertain beliefs. And if there were no certain beliefs, then I don't think we could be justified in believing anything, not even in a probabilistic way. Because if I believe that something is probably the case, this belief is only justified if I am certain regarding my method of ascertaining probability. In other words, probabilistic beliefs require certain beliefs to justify them. If you disagree on this point, I will explain my reasoning further.

So, if it is possible that x is epistemically justified in believing P, and y is epistemically justified in denying P, then it is possible that P is both true and false. But this is a contradiction. I don't think a contradiction is any less contradictory if it is asserted as a possibility than if it is asserted as an actuality.

In order to avoid the contradiction, you could argue that epistemic justification is impossible for humans. But knowledge requires epistemic justification, so if epistemic justification is impossible for humans, so is human knowledge. But if human knowledge is impossible, then radical skepticism ensues. But I don't think radical skepticism is a tenable position, since it refutes itself. I can't know that I know nothing because then I would know something.

Thus, I think the only reasonable thing to do is to reject premise 3. Gettier cases aside, different thinkers cannot both be epistemically justified in affirming and denying the same proposition. It doesn't matter whether one thinks by means of a brain and the other the other thinks by some other means.

Now, you might ask, how are we justified in believing that thinkers who think without brains would come to the same conclusions as us? After all, we have no idea what it would be like to think without a brain. Well, it's not that they'd necessarily come to the same conclusions, but rather that, if we were both epistemically justified in our conclusions, we would agree. And, unless we want to be radical skeptics, we have to admit that we can be epistemically justified in at least some of our beliefs. So we must reject premise 3 and affirm the contrary: namely, that 1) we are epistemically justified in some of our conclusions and 2) if thinkers who thought without brains were epistemically justified, they would come to the same conclusions.

Well, yes and no - we are local, but we can aspire towards the universal. It's just that we can never totally reach it. To be human means to be subjective and limited, but there are great variations in how subjective and how limited. — hwyl

I think I agree if you mean that no philosophical system can ever be truly universal, in the sense that it comprehends the fundamental structures of reality. Philosophical systems can represent reality more or less accurately, but none can fully comprehend it. So if universality means comprehensiveness, then yes, I agree that universality can only be approached, not realized.

However, if you mean that no single proposition can be universal, then I disagree. I think that the principle of non-contradiction, that the same thing cannot both be and not be in the same respect, is a universal truth. It doesn't come anywhere close to comprehending reality in its totality, but it comprehends one aspect of reality, namely, that reality cannot contradict itself. Non-contradiction is just the most obvious example of a universal truth, but there are others as well. In fact, I think all true propositions are universally true. If it's true that I woke up at 8am on June 7 2021, then it is true at all times and in all places and for all observers. Truth, I believe, is universal by nature, in the sense that the same proposition, insofar as its articulated with sufficient clarity, cannot be true for some and false for others.

I just think that every philosophical enquiry should start from history, from the narrative of how these particular meanings and concepts emerged in a particular place and in a particular continuum of slow time. — hwyl

I agree that all philosophers should learn about the history of ideas. But I don't think it's necessary for every philosophical work to be extremely attentive to history. If I wanted to write a book, for instance, arguing in favor of virtue ethics, it would probably good and constructive if I included analysis of the development of different ethical theories across the history of philosophy. But I don't think this historical analysis would be strictly necessary for the book to be worth reading. In fact, it might in some cases be better to cut the historical analysis for the sake of brevity.

Aquinas writes in his Contra Gentiles book one ch. 23 that "bodily things receive their accidents through the nature of their matter and cause them from their substance"

So matter can be in any form but each discrete thing has a form that makes it itself. Yet how is the form to be understood? — Gregory

Bodily things, according to Aquinas (he gets this from Aristotle) are composites of matter and form. These composites are substances. The form gives the bodily substance its nature and determines the kind of substance it is. If a substance is a tree or a dog or a stone, this is due to its form. The form is in the matter, not vice versa. So, to answer your question, each discrete bodily thing does not have its own, unique form that makes it itself. All dogs, for instance, have the same canine form. Matter individuates form. So many bodily substances can exist, each with the same canine form, but with different material substrata. This is, I think, why he says bodily things receive their accidents through their matter. If one dog is brown and another is white, this is not because they have different substantial forms, but because, as individuals, they receive different accidents, namely browness and whiteness respectively. And it is matter, not form, that makes them individuals and thus allows them to receive these diverse accidents.

He writes in ch. 55: "Our intellect cannot understand in act many things together. The reason is that, since intellect in act is its object in act, if intellect did understand many things together, it would follow that the intellect would at one and the same time many things.."

Why? Because the world is in us and we are in the world in the same respect. Aquinas is far more Kantian than you would expect him to be. — Gregory

Perhaps I'm misunderstanding you, I think you may be misinterpreting Aquinas here. In saying that objects are in the intellect, he is not saying that the known world of objects is existentially dependent upon and structured by the mind, like Kant does. Aquinas is not an idealist of any variety. He believes in a mind-independent external world that we can know through our senses. Rather, I think that what Aquinas means by 'the object in act' is the intelligible object in act. Each object is potentially intelligible, but it only becomes actually intelligible when it is understood by an intellectual being. Thus, the intelligible object in act is the object considered in the intellect. Objects subsists outside the intellect and in the world, but their intelligibility is only actualized when an intellect apprehends and considers them. Now the intellect becomes the things it considers. So if I am considering a tree, the act of my intellect in considering the tree is the act of the tree as an intelligible object.

Perhaps I'm misinterpreting you, but it sounds like you are saying that there are no universal truths. Each of us, being born at a particular time in a particular culture, only has access to what seems true from our limited and highly conditioned perspective. Am I correct that you are saying this? If so, then it seems that you subscribe to a kind of relativism, perhaps cultural relativism.

I don't think relativism can be right. Firstly, because there are many universal truths that I think we do have access to, such as the principles of logic and perception. Secondly, because relativism is self-refuting. If there were no universal truths, it would not be a universal truth that there were no universal truths.

I'm guessing that I'm missing something in what you're saying. But I hope my point is at least useful for clarificational purposes.

I don't think he claims this to be the logical conclusion of his argument. It is more like, having cleared the ground, he is venturing a plausible hypothesis. As any narrative that describes events and processes, it must rely on causal notions in order to make any sense. But he already admitted that causality is ingrained in our thought process and is indispensable for sense-making. — SophistiCat

I suppose it makes sense that constant-conjunction is only a hypothesis, although I haven't read Hume recently enough to judge whether or not he phrased it as a mere hypothesis. However, the hypothesis seems to entail that causality is real, and if causality is real in psychology, it might as well be real in physics and other realms also. But I guess the point of the constant-conjunction hypothesis might not be to reject the reality of causality. Rather, the point might be to show that, given the inductive manner whereby we arrive at the notion of causality plus the problem of induction, we cannot have certain knowledge regarding the reality of causal relations. But as I've argued elsewhere in this post, I think causal relations are indispensable to the justification of belief and hence to the existence of knowledge. So skepticism regarding causal relations, I've argued, entails skepticism regarding all knowledge i.e. radical skepticism. And I think radical skepticism is a self-defeating position, since if knowledge is probably impossible, then one probably cannot know whether or not knowledge is possible, in which case one is not justified in believing that knowledge is probably impossible. If my arguments are sound, then causal skepticism can be refuted by retorsion.

It may be that there is no such thing as causation, or that causation is inexplicable, or that there is an as-of-yet unknown means to explain causation. If one of these is true then I don’t think Hume’s argument fails. — Michael

In the original post and in my response to you, I differentiated Hume's causal skepticism (some in the thread have argued that Russel and I are wrong to attribute this to Hume, but so be it), which self-refutingly explains our causal beliefs by appealing to constant conjunction, and non-explanatory causal skepticism, which doesn't attempt to explain our causal beliefs at all. And I made two arguments 1) non-explanatory causal skepticism fails to explain key facts about reality 2) non-explanatory causal-skepticism is specifically necessary to account for human knowledge. By key facts about reality, I just mean things like why are cheetahs faster than dogs, or why do people slip on wet floors, or why is it dangerous to drive blindfolded. Without at least some vague notion of causality, I don't think you could answer any of these questions.

As for 2), why non-explanatory causal-skepticism is specifically necessary to account for human knowledge, refer to the arguments in my previous posts. If there is no causation, I argued, there can be no knowledge. So if causation is inexplicable, then knowledge is inexplicable, and we can't explain the difference between justified knowledge and unjustified belief. If there is an as-of-yet unknown means to explain causation, then the means of explaining what makes some beliefs justified and others not justified is also as-of-yet unknown, so we cannot know the difference between knowledge and unjustified belief. All three of these conclusions would invalidate all of our knowledge and lead to radical skepticism. For if we can't know anything, we have no justification to belief anything. If radical skepticism is true, then philosophy is futile. So I think radical skepticism is also self-refuting, since it can't justify itself.

After all, I don’t need to provide an alternative to a God of the gaps to argue that a God of the gaps explanation is either false or unjustified. — Michael

I think that depends on what you mean by God of the gaps. I think there are valid and invalid gap arguments. An invalid gap argument would go like this: 1) P is a fact that we have no explanation for, 2) if Q were true, Q would explain P, 3) therefore, Q is true. But a valid gap argument would be: 1) either P is true or Q is necessarily inexplicable, 2) If Q is necessarily inexplicable, then it is impossible to provide a coherent account reality, 3) therefore P is true. My argument is of the latter kind, not of the former kind: 1) Either it can be explained why certain things are causally related, or human knowledge is necessarily inexplicable, 2) if human knowledge is necessarily inexplicable, then it is impossible to provide a coherent account of reality, and radical skepticism ensues, 3) therefore, it can be explained why certain things are causally related, namely, why the mental act of justification causes belief to become knowledge.

And in neither case is Hume making an attack on the world, that there is no such thing as causation, or that there is no such thing as morality. Rather, he is making an attack on overblown rationalism that thinks it can make the world conform to thought, instead of conforming thought to the world. — unenlightened

If that's all Hume were trying to do, then I would happily get behind him. But I'll leave the discussion of Hume's belief system to others. Unfortunately for people like me who enjoy speculation more than research, an ism that takes its name from a philosopher is probably less nuanced and compelling than the ideas of the philosopher it's named after.

No, I don't think his skepticism is self-refuting. His argument seems to be that 1) we only ever observe X following from Y and that 2) it is invalid to infer from this that Y causes X. — Michael

I agree that those two premises are not refuted, at least not directly, by the conclusion that we have no knowledge of causality. But as you seem to admit, the conclusion does refute Hume's (apparent?) notion that we can reasonably identify constant conjunction as the source of our belief in causality and our expectations regarding future events. And in the the third and fourth paragraphs of my original post, I argued that a form of causal skepticism that doesn't offer an explanation for our causal beliefs is explanatorily inadequate, and should thus be rejected as unsound. Any belief that makes it impossible to explain key facts about reality, I think, ought to be rejected.

And maybe the argument you presented is indirectly refuted by non-explanatory causal skepticism. For if we don't have a way of explaining why we believe some things to cause other things, we can't rationally distinguish between causal and non-causal relations. Thus, we cannot justify believing in any causal relations, whether these causal relations are real and physical or merely intuitive and psychological. But the idea of knowledge seems to presuppose at least some form of causal relation. For the causal realist, the mental act of justification really causes a belief to become an item of knowledge. For the Humean skeptic, the fact that the mental act of justification always precedes beliefs becoming more firmly held suffices to differentiate, at least from a psychological standpoint, mere belief from what we call knowledge. But for the non-explanatory skeptic, who denies constant conjunction as an explanation for our causal intuitions, nothing seems to differentiate knowledge from unjustified belief. Therefore, if non-explanatory skepticism is true, we can have no reason to believe either of the two premises you presented. Can you find a flaw in this argument? If not, then perhaps causal skepticism is self-refuting whether or not it tries to explain causal beliefs, although non-explanatory causal skepticism refutes itself in a less direct way.

However, I don't think it is fair in this case to accuse him of illicitly helping himself to the very ideas that he questioned. That Hume imagined impressions being caused by their objects is a speculation. — SophistiCat

I seem to remember Hume illicitly helping himself to causal notions, but perhaps my memory is foggy and or my reading was uncharitable. But others in this thread seem to be debating exactly what Hume meant, so I will leave that to them.

Any philosophical approach that utilizes a notion of refutation is a form of skepticism. — Joshs

Are you saying that philosophical skeptics always employ a kind of self-destruct mechanism that they believe is rooted within the structure of human reason? For instance, skeptics will often point to paradoxes as evidence that reason cannot offer a consistent explanation reality. Is Hume, by showing that belief in causation is unreasonable, showing that any kind of belief, including belief that belief in causation is unreasonable, is unreasonable? This reminds me of the Wittgenstein quote about the ladder which, once it gets you to the final conclusion, you must kick away. Once reason succeeds at undermining itself, you can just stop using reason, so you don't need reason to justify your skepticism. Is this what you're getting at?

In other words, I take it, if Hume was correct, we couldn't actually think or make judgements; we'd have, at best, the cognitive capacity of a newborn, or someone with an acute neural disorder, because of the role of the mind in synthesising and constructing experience and sensations into a meaningful whole within which judgement is possible. And we don't naturally see that, because we see with it, or through it. That's why Kant can claim that in some basic sense, Hume must assume some of the very things that he purports to doubt. That's my gloss. — Wayfarer

That makes sense. If the concept of causality is necessary to intelligibly structure experience, then all experience must presuppose it in some way. And all experience includes the experience of formulating a philosophical theory, like Hume's, that attempts to explain away causal relations.

I think Kant's notion of causality might also be self-refuting, but I'll save that for a future post.

The fact is that, where psychology is concerned, Hume allows himself to believe in causation in a sense which, in general, he condemns.

That's exactly what I'm trying to get at. Very well put.