Do you have a response for people who do not take Wittgenstein's writings as gospel? — Art48

Yes, there is an alternative to praying at the altar of Plato, it is appreciating human’s incredible ability to create a form of life like mathematics.

The Pythagoreans were shocked to discover that the square root of 2 was irrational.It is an eternal fact that the square root of 2 cannot be expressed as a ratio of two whole numbers. That fact was true before the Pythagoreans discovered it and it will be true for all eternity. You seemed to be taking the Mathemetical Formalism route, which is a minority position among working mathematicians, most of whom accept Mathematical Platonism. — Art48

From Wittgenstein's "Remarks on the Foundation of Mathematic"

I 168, "The mathematician is aninventor, not a discoverer."

II 2 "But the mathematician is not a discoverer: he is aninventor."

II 38 "From the fact, however, that we have an employment for a kind of numeral which, as it were, gives the number of the members of an infinite series, it does not follow that it also makes some kind of sense to speak of the number of the concept 'infinite series'; that we have here some kind of employment for something like a numeral. For there's no grammatical technique suggesting employment of such an expression. For I can of course form the expression: "class all classes which are equinumerous with the class 'infinite series'" (as also: "class of all angels that can get on to a needlepoint") but this expression is empty so long as there is no employment for it. Such an employment is not: yet to be discovered, but: still to be invented."

V 11 "If you want to know more about the series, you have, so to speak, to get into another dimension (as it were from the line into a surrounding plane).-But then isn't the plane there, just like the line, and merely something to be explored, if one want to know what the facts are? No, the mathematics of this further dimension has to be invented just as much as any mathematics."

From Wittgenstein's Lectures on the foundations of Mathematic

"One talks of mathematical discoveries. I shall try again and again to show that what is called a mathematical discovery had better be called a mathematical invention. In some of the cases to which I point, you perhaps be inclined to say, "Yes they had better be calledinventions"; in other cases you may perhaps be inclined to say, "Well, it is difficult to say whether in this case something has been discovered or invented."

Wittgenstein's position is an outcomes of his later views on language and meaning, exploring how these symbols become "alive with meaning." For him, Platonic views of mathematics lack utility due to offering no explanatory power and leading to confusion.

We are truly naive realists if we believe that the way we experience and understand the world to be is exactly the way it really is independently of us. — Janus

I do not understand why some do not see or feel the emptiness of this description. The tone reminds me of negative theology, let us get to “Reality” by saying what it is not. But we never can get there, and they come up with equally empty slogans like if only we can get a “view from no where” or if we only can get “outside ourselves”. This move seems so innocent to use words that we are so familiar with yet are used in such unfamiliar ways.

But the indirect realist will say, “Wink, wink you get what we are saying.”

Yep, pure nonsense!

Would not basic arithmetical facts be true in all possible worlds? — Wayfarer

Interesting question. There is a lot to unravel here when using terms like "facts", "true", and "possible worlds" which will lead to much confusion.

1. What is an "arithmetical fact"? That we use a human invented symbolism like "2+2=4" and that this has rules of use, and has application in our world. OK. Or, do you mean "2+2=4" is a fact because it corresponds to some eternal idea. I reject this later position as metaphysical nonsense.

2. What make "arithmetical facts" true? That we use these human invented symbolisms like "2+2=4", we agree on the use, we agree on judging correctness. Ok. Or, do you mean "2+2=4"is true because it corresponds correctly to some eternal idea. I reject this later position as metaphysical nonsense. (As Wittgenstein says in PI 241"So you are saying that human agreement decided what is true and what is false?- It is what human beings say that is true and false; and they agree in the language they use. This is not agreement in opinions but in form of life."

3. Lastly, what to make of "true in all possible worlds"? First, I like what Saul Kripke said in N&N, "In the present monograph I argued against the misuses of the concept that regard possible worlds as something like distant planets, like our own surroundings but somehow existing in a different dimension, or lead to spurious problems of 'transworld identification." and "'Possible worlds' are stipulated, not discovered by powerful telescopes." Are you thinking this very thing by discussing other sentient being across the universe? Second, is it not hard to imagine a fictitious natural history where human do not have this symbolism, its use, its general agreement in judgment? If so, it would not be "true in all possible worlds".

"'To be practical, mathematics must tells us facts.'-But do these facts have to be, the mathematical facts?-But why should not mathematics, instead of 'teaching us facts', create the forms of what we call facts?" From Remarks on the Foundation of Mathematics, Wittgenstein.

It is a big step and probably the cause of much discussion in this thread. That 2+2=4 is eternal is one thing. — Art48

atever word someone wants to use), it's difficult to see how it could go out of existence or cease to be. — Art48

Let us see if we can provide a clearer path to seeing one’s way out of this conceptual muddle. I will use the “2+2=4” example.

1. We needs to recognize that humans invented the symbolism of “2+2=4”. Other symbolism could be used, and I am sure other humans have used different symbolism.

2. What makes these symbolisms the same is how they are used by humans. It is not that they refer to the same eternal objects.

3. “2+2=4” symbolism will cease to exist if there are no more humans using these symbols for any purpose. In fact, they will cease being symbols.

4. But one could say, even if there are no more human around, there could be two trees, etc. Yes, but there is not a tree and another tree, and “two-ness”, just a tree and another tree.

5. Last step, let us imagine we have no symbolism, nor anything else in the universe to count. What is left to articulate? Remember, humans do not exist, our symbolism does not exist, and the physical universe does not exist.

I would say this is easier or as easy “to see” as adding “Mindscape”/“Platonic realms”. And if we value parsimony, dropping “Mindscape/Platonic realms” would be wise.

So my argument is that they're real, because they're the same for all who think, but they're not strictly speaking existent. — Wayfarer

And it would be unreal if they’re different for all who think? But this would just be different ideas. Or, someone is thinking the same thing but the idea is different compared to someone else thinking the same thing? This does not make sense. Austin said the following about “real”, “Real, is also a word whose negative use “wears the trousers” (a trouser-word)”

But that is a reification - there is no literal 'realm of natural numbers', although it is conceptually real. — Wayfarer

Now I am curious, what is an example of something that is conceptually unreal?

Colours and smells are not mind-independent properties of objects but are products of brain activity that result from (usually) external stimulation. — Michael

This seems problematic to say. Let take a simple scientific definition of color. “Color is that portion of the visible spectrum of light that is reflected back from a surface. The amount of light that a surface reflects or absorbs determines its color.” Notice in this definition there is no appeal to mind or brain. Light is not being produces by the brain/mind, but is independently being produce outside the brain/mind.

What occurs inside the brain, when stimulated by a particular color of light can as well be studied. But scientists don’t study the brain by opening it up to find “colored objects” dancing around.

As for what occurs in the mind when stimulated by a particular color of light, not sure where to begin to make sense of this claim, like how does the physical interact with non-physical. I think we are probably in the realm of grammatical fictions where the word “color” mistakenly is thought to name a object within the mind.

Your eyes don't see things. Your ears don't hear things, and your fingers don't feel things. Your central nervous system sees, hears and feels. There clearly is an interface between the CNS and the world. — frank

When I enter a room and turn the light switch off, I do not see, “my eyes do not see”, and “my nervous system does not see”. Clearly, there is an interface between the light switch and the world.

Long live “indirect realism”.

Well, is determinism theoretically possible? If we want to be fair, we should not assume either is the established Truth. But this answer to the question “Is libertarian free will theoretically possible?” seems to assume or accept determinism to be the Truth in which free will must be analyzed to fit in this world view.

But this can be easily flipped, and one can assume or accept free will to be the Truth and that determinism must be analyzed to fit in with this world view.

If you say, of course determinism is the Truth, we see it at work everyday of our lives(billiard balls chemical reactions), etc, it is actual and thus theoretical possible. Sure, alternatively, we can say free will is the Truth, we see it at work everyday of lives(who will I love, will I commit that crime, etc), it is actual and thus theoretically possible.

Just as there is one "landscape" (i.e., the physical world) where anyone can roam, there is one mindscape where any being capable of thought can roam. — Art48

From Augustine’s Confessions where he gives an account of how he had ‘learnt to speak’:

“I noticed that people would name some object and then turn towards whatever it was that they had named. I watched them and understood that the sound they made when they wanted to indicate that particular thing was the name which they gave to it, and their actions clearly showed what they meant.”

So Augustine was questioning, observing, inferring, concluding, what you would call “thinking”, before he had learned a single word.

Wittgenstein in PI 32 says “Augustine describes the learning of human language as if the child came into a strange country and did not understand the language of the country; that is, as if the child could already think, only not yet speak.”

This picture of a “Mindscape” being accessible to a child assumes this very same thing. That the child can learn any idea like “cause”, “intention”, “hope”, without learning any language from anyone. That they can dive into their private world and figure out these ideas without any guidance from anyone whatsoever. And even if they wanted to, others have no access to this private world to provide any guidance.

If all humans could access the Mindscape, would it qualify as a "private world"? — Janus

Do babies enter the Mindscape,? Infants? Children? Adolescents? Adults? A certain IQ level? Cultural background?

How would anyone teach a language to describe this “private world” they so call “accessed”? No one has access to anyone else's “private world” because it is inaccessible. But we got the public world.

A person who does mathematical research, writes stories, or meditates is an explorer of the Mindscape in much the same way that Armstrong, Livingstone, or Cousteau are explorers of the physical features of our Universe. The rocks on the Moon were there before the lunar module landed; and all the possible thoughts are already out there in the Mindscape.” — Art48

We first learn of ideas and how to think not by introspection, but by our fellow human beings, learning a rich intellectual tradition handed down from generation to generation. This picture of "Mindscape" would make you think we could isolate ourselves from others, and tap into the "Mindscape" to learn our ideas, and that there is no need to interact with another human being. It starts first by learning of ideas from other humans, not by private introspection into alternate realities. Do we introspect? Of course, with ideas that are learned in a public world taught by our fellow humans.

The contribution from your fellow human beings and the world around us is a better explanation of thoughts/ideas than appealing to introspection of a private world call "Mindscape."

For instance, if the Earth and everyone on it disappeared tomorrow, if all memory of the play Macbeth vanished, would the play still exist in some form or another? Yes or no? Before answering, consider that the basic question is about all ideas and thoughts. If the Big Bang had never occurred, would the thought “two plus two equals four” exist? Yes or no? — Art48

Does this make any sense? Another way to look at it, if all ideas and thoughts did not exists in the "Mindscape"; would humans be able to think about these ideas at all? If one says, "yes" this is exactly the implication, humans would not be able to think these ideas at all. Can anyone coherently explain how this is so? It reminds me that this problem is similar as the one brought up by Elisabeth of the Palatinate to Descartes with regards to the "Mind-Body" interaction.

I do not think it makes sense to use the word “seeing” when we talk about “when we sleep”. This is done by analyzing the grammar of “dreaming” and “sleeping”.

Of course, scientists can explore all they want when it comes to what is occurring in the brain when we sleep.

However, as for what psychologists are doing with regards to “dream” is a somewhat precarious.

The whole time we are staring at the back of our eyelids. — NOS4A2

If you closed your eyes, I would not say you are staring at all.

No doubt I'll be corrected if wrong, but I think the reference is to dreaming. — Janus

Yeah, even so, this does not make sense. Imagine a child wakes up from a deep sleep and says to their parent, “I just saw a pink elephant in my room.” The parent will assure the child that they did not see a pink elephant, and will correct the child and say something like ‘No, you dreamt that you saw a pink elephant’. Being in a deep sleep logically excludes that one sees anything.

I see things when I am asleep. — I like sushi

This must be quite a skill. If I find you sleeping and held a stick in front of your face you would able to see it. I bet you are peeking.

One historical mistake certain philosophies have made is this search for certainty instead minimizing error for a purpose.

What I'm saying is, he still believes that the "world is [still] all that is the case," — Sam26

I am not sure. Let us look at two quotes that may support this view, and two quotes that may not support this view.

Not Support;

1. From PI 241, "So you are saying that human agreement decides what is true and what is false? It is what human beings say that is true and false; and they agree in the language they use. That is not agreement in opinions but in form of life."

2. From PI Part 2 xii, "If formation of concepts can be explained by fact of nature, should we not be interested, not in grammar, but rather in that in nature which is the basis of grammar? Our interest certainly includes the correspondence between concepts and very general facts of nature. (Such facts as mostly do not strike us because of their generality.). But our interest does not fall back upon these possible causes of the formation of concepts; we are not doing natural science; nor yet natural history-since we can also invent natural history for our purposes. I am not saying: if such-and such facts of nature were different people would have different concepts (in the sense of a hypothesis). But; if anyone believes that certain concepts are absolutely the correct ones, and that having different ones would mean not realizing something that we realize-then let him imagine certain very general facts of nature to be different from what we are used to, and formation of concepts different from the usual ones will become intelligible to him."

Support;

1. OC 505, "It is always by favor of Nature that one knows something."

2. Culture and Value, "Life can educate one to a belief in God. And experiences too are what bring this about; but I don't mean visions and other forms of sense experience which show us the 'existence of this being', but e.g. sufferings of various sorts. These neither show us God in the way a sense impression shows us an object, nor do they give rise to conjectures about him. Experiences, thoughts, -life can force this concept on us. So perhaps it is similar to the concept of 'object'.

Wittgenstein's oscillates between two views, human's contribution to concepts, and Nature/Life/World's contribution to concepts. So "The world is all that is the case.", I believe Wittgenstein does not consider the human contribution in the Tractatus, but that there must be an isomorphic relation between the logic of language and the logic of the world to make sense. However, I do not believe he gives up on this idea that our concepts are, at times, accountable to the world we live in.

My understanding of his later philosophy is that he still believes there is a limit to what can be sensibly said, which is why I think T. 1 is still something that he holds on to. — Sam26

Not is some general philosophical sense. Only that there is agreement in a language game and form of life. This is agreement in judgment and action. This is shown by describing these forms of life.

It is not coming up with some metaphysical theory like is done in the Tractatus explaining the demarcation of sense and nonsense.

This is not continuous but abruptly different approaches. One is a general metaphysical theory. The other is describing and sticking to examples.

Yeah both are exploring “what is meaningful to say” but if that is the criteria for calling something continuous, then you could say that any philosophy of meaning is continuous with any other theory of meaning.

I like to avoid the metaphysical views of knowledge and go with a more pragmatic one.

Humans have knowledge when they demonstrate the application.

For example, Do you have knowledge of riding a bike. Well yes I do let me show you, and the human proceeds to ride the bike.

For example, do you know the theory of special relativity. Well yes let me explain it, discuss the implications, and set up experiments to show you the data.

One of the common misunderstandings of Wittgenstein’s later writings is that he rejected the Tractatus. And while it’s true that Wittgenstein did reject some of his earlier premises (e.g., that there was a one-to-one correspondence between names and simple objects in the world – more on what names and simple objects are later), he did not reject the Tractatus in total. This is not to say that he wasn’t a harsh critic of the Tractatus, because he was. It’s only to say that there is a continuity of thought between Wittgenstein’s early and later thinking. — Sam26

One of the foremost Wittgenstein's scholars would disagree with this assessment. Norman Malcolm, in Nothing is Hidden, listed 15 positions in the Tractatus that he believes were rejected in Wittgenstein's later thinking.

"1. That there is a fixed form of the world, an unchanging order of logical possibilities, which is independent of whatever is the case.
2. That the fixed form of the world is constituted of things that are simple in an absolute sense.
3. That the simple objects are the substratum of thoughts and language.
4. That thoughts, composed of "psychical constituents', underlie the sentences of language.
5 That a thought is intrinsically a picture of a particular state of affairs.
6. That a proposition, or a thought, cannot have a vague sense.
7. That whether a proposition has sense cannot depend on whether another proposition is true.
8. That to understand the sense of a proposition it is sufficient to know the meaning of its constituent parts.
9. That the sense of a proposition cannot be explained.
10. That there is a general form of all propositions.
11. That each proposition is a picture of one and only one state of affairs.
12. That when a sentence is combined with a method of projection that the resulting proposition is necessary unambiguous.
13. That what one means by a sentence is specified by an inner process of logical analysis.
14. That the pictorial nature of most of our everyday propositions is hidden.
15. That every sentence with sense expresses a thought which can be compared with reality."

But then if nothing is external, the difference between internal and external dissipates. — Banno

Maybe, they will come up with some fancy existential word like “Other” rather than “external.” At this point, just plug the fly bottle and throw it away.

You’re just playing word games. — Michael

Not word games, this is how we learn and understand the meaning of the word “dream”

Because we see and hear and feel things when asleep. That's what dreaming is. — Michael

When we sleep our eyes are closed, we do not see things while we sleep. So we hear, maybe, especially if we are a light sleepers, any noise might wake us up. Do we feel, again maybe, we hear someone who is moaning as if they are in pain. When we wake up we may report seeing many things, however, we know this is not true because none of the events reported happened, that is why we call it a dream.

What's the difference? We know that the external world is constituted of things like atoms and electromagnetic radiation. We know that electromagnetic radiation is reflected by bundles of atoms into our eyes (which are themselves bundles of atoms). This stimulates brain activity (which is itself bundles of atoms). This triggers the occurrence of visual or auditory or tactical experience. What else is there to add to this? — Michael

Not “sense data”. What is the distinction between metaphysics and scientific explanations. Let’s start with the following definition of metaphysics: “Derived from the Greek meta ta physika ("after the things of nature"); referring to an idea, doctrine, or posited reality outside of human sense perception.” Sure does not sound like what science is suppose to investigated. Ok, now let’s look at a definition of science: “the systematic study of the structure and behavior of the physical and natural world through observation”. Looks like different fields of study. Pragmatically speaking, how do they differ? Well one way scientist will investigate is the utilization of labs, instruments, experiments, and/or data analysis. What about philosophers? They construct arguments. “Sense data” is an argue from ideas of hallucinations and veridical experiences (Argument from Illusion)

Another example of sense data having explanatory power is that of dreaming or hallucinations. I see and hear and feel things when I dream. I'm not seeing or hearing or feeling some external world stimulus. — Michael

This is a conceptual confusion. What we humans do is report that we have dreams. That is how we come to understand this term. I would encourage anyone who wishes to understand this argument to read Norman Malcolm’s book “Dreaming”.

That is the very question that gave rise to the distinction between direct and indirect realism. We wanted to know if the world "really is, objectively" as it appears to be. The direct realists argued that the world "really is, objectively" as it appears to be, because we see it "directly" (whatever that means). It therefore follows that if the world isn't "really, objectively" as it appears to be, then we don't see it "directly" (whatever that means). — Michael

Using words like “direct” and “indirect” have meaning is everyday use. However, the problem here is that both the direct and indirect realist misuse they terms and create great deal of confusion when moved from its ordinary use (as I tried to show with my camera/tree example)

The irony here is that you (and many others) appear to be using direct realist terminology but accept the indirect realist's conclusion regarding the disconnect between how things appear and how they "really, objectively" are. — Michael

I would not say I am arguing for the direct realist position but I am arguing against the metaphysical position of both the direct and indirect realist. Only that the indirect realist has more to argue against, their confusion runs deeper. As for what “appear to be so” vs “what it is really”, again when philosophers take these ordinary terms for their ordinary use, that is when the trouble begins.

I think it has explanatory power in the case of the dress that some see to be black and blue and others see to be white and gold. Each person can be looking at the same photo, in the same lighting conditions, and from the same perspective, but given their differences in eye and brain structure, the quality of their visual experiences differ. — Michael

To be clear, I am not arguing the scientific description/explanation of perception but only the metaphysical explanation. From your passage it is not clear which of these you are trying to argue.

One person sees white and gold, and so uses the phrase "white and gold" to refer to what they see. The other person sees black and blue, and so uses the phrase "black and blue" to refer to what they see. In a quite understandable sense, each person is seeing something different. So if each person is seeing something different, despite the shared external world stimulus, then they aren't seeing that shared external world stimulus. — Michael

Many times in human experience, two people can disagree on what they see for many reasons without appeal to "sense data". For example, maybe when someone looks at a duck-rabbit picture they only report seeing a rabbit because they never experience every seeing a duck, thus, there is no need to use "sense data" to explain. Another example, I show a rectangle where at one end it is one color transitioning to the other end into another color. At both ends, most people will judge and agree what the color is. But as we transition we will find less agreement in the middle and maybe sometimes some will not commit to any color. Do I need "sense data" to explain this or just the fact that I created an example to solicit different responses. But maybe thru training, I might eventually get greater agreement. Goodbye again "sense data". Or, scientifically, human beings differ biologically from person to person. Like a color blind person who has difficulty judging between red and green. This is discovered not by asking someone, can you explore your sense data and tell me what color you see, but designing publicly observable samples to see how one judges against accepted responses.

Historically at least, direct (or naive) realists would argue that colour, shape, sound, taste, etc. are properties inherent in external world objects, and indirect realists would argue that they're not. And I think our current understanding of the world, at least with respect to colour, sound, and taste, agrees with the latter. — Michael

Yeah but there is a problem the indirect realist seems to create. Let us say we have a tree outside of a house. We place a video camera to focus on the tree. We hook up some cables and move them into the house where we connect them to a video screen. When I look at the screen, I perceive the image of the tree. I can say "I am looking at it indirectly." Is that because I have this casual train from light to the lens of camera, to the electrons flowing in the wires, etc. etc. etc. Or because, I can go outside and "directly" perceive the tree. But, the indirect realist says, "this is not the same because we do not know what the tree "really" looks like to compare, we only have our "sense data". This makes no sense because the indirect realist suggests that if only we could "directly perceive" something where we are not involved in the perceiving. It is like saying, "what is the color of the tree when there is no light?"

He argues that no one can ever never know the private perception of another, but can only infer it from their behaviour. — RussellA

This is incorrect. Wittgenstein is saying that this picture of naming something private drops out as inconsequential in terms of how we understand what is being communicated.

I would directly perceive the stick figure, and the child would directly perceive the stick figure. This would mean that I would know that my private perception was the same as the child's private perception, and vice versa. — RussellA

This is incorrect. See above. Both are perceiving, talking about a publicly shared object. Not providing proof of what they are supposedly perceiving privately.

Imagine they see a duck. As before, they look into the distance past the picture and will see not one object but two sense datum. This means that it is not the object they are directly looking at but the sense datum. Then, when they look at the picture, it may appear that they are directly looking at an object, but in fact they are directly looking at sense datum. — RussellA

But they cannot distinguish between the two “sense datum” of the picture, they are the same. The positing of “sense datum” does not explain why they report a rabbit one time and a duck another. So, “sense datum” has no explanatory power in this case.

I have attempted to show indirect realism: 1) Is incoherent based on this idea of "directly perceiving sense data" because it was shown to be a grammatical fiction. 2) cannot be determined to be truth, in principle, due to the nature of "sense data" being a private, inaccessible experience. 3) inadequately claims to universally applied to all human beings if based on hallucinations which most do not experience. 4) pragmatically does not differ from direct realism in terms of establishing knowledge claims.

Next, I like to show at least one example of human beings directly perceiving something which an indirect realist would wrongly claim to be an inference. This is to show at least it is plausible this idea of direct realism. Also, I like to show at least one example of an illusion which conflicts with this idea of human beings must have "sense data" to explain such phenomenon.

a. I draw a stick figure of a person from my imagination. I show this picture to a child and ask her "what to you see?" The child may reply, "I perceive a stick figure of a person." Can we not claim that the child directly perceives a picture of a stick figure? It seems incorrect to say this is an inference from my perception of sense data. I drew the figure, I know exactly what I intended to draw. The child reported exactly what I drew. It is difficult for the indirect realist to say, "Well, we cannot say what is behind this sense data of the picture of the stick figure" because the author of the creation is telling us what it is, (unlike "Mother Nature" who seems to hide her secrets according to the indirect realist).

b. The famous picture of the "duck-rabbit" is an illusion. If presented to someone, they could see the picture as a rabbit, or, another time, see the picture as a duck. However, could we not say the what we perceive is the same figure in both cases? If so, the positing of sense data has no explanatory power in this case to explain this illusion.

"It’s wise for Direct Realists to concede that for humans, and for percipients physiologically
like us in the actual world, perception involves a long and complex causal series of events, and that perception is indeed dependent upon the condition of the eyes, of the optic nerve, and of the brain, upon the nature of the intervening medium, and so on."

"But perception involves a long and complex causal series of events. For instance, light quanta are reflected or emitted from an external object, the light quanta then travel through an intervening medium (e.g., air and/or water), they then hyperpolarize retinal cells by bleaching rhodopsin photopigment molecules, and then a very complex series of physiological processes takes place in the eye and in the brain eventuating in perception." — RussellA

Sure, for me to perceive the tree, I need light. For me to perceive the tree, I need to have my eyes open. And this is suppose to turn me into indirect realist because of the causal train of events.

So, if there is no light the tree does not have a color, when there is light the tree has color. But to be a direct realist, it has to have a color for me to directly perceive no matter if there is light or not? Yes, according the indirect realist, it is part of the casual process.

Based on their logic, the indirect realist does not have to introduce the mind, brain, nerves, sense data, etc to refute the direct realist. They got light on their side.

But I do not think the direct realist should be concerned about how we perceive, but how we learn and use the word “perceive”, how we make judgements about what we perceive, or how we gain knowledge from what we perceive.

Son: Dad

Dad: Yes, son

Son: Do I have sense data?

Dad: Sure, let me show you. Look at that tree. Now, press you eye like this and you will see two trees.

Son: Like this?

Dad: Yes

Son: But I don't see two trees.

Dad: You must be doing it wrong. Let me press them.

Son: Ouch! That hurts. And I still don't see two trees.

Dad: Well son, I guess you don't have sense data. I guess you are one of the few actual direct realist.

Son: Wow, that's neat. What are you?

Dad: An indirect realist. By the way, what does the tree look like?

Son: It looks like ..........

Dad: Funny, that is how it looks to me.

Wittgenstein in PI is more an Indirect Realist than a Direct Realist — RussellA

I think later Wittgenstein resist being labeled an Idealist or Realist, or anything in-between. May be difficult to argue this sufficiently in a posting, but I will give it try.

From Philosophical Investigations(PI)

P. 402, he says the following, "For this is what disputes between Idealist, Solipsists and Realist look like. The one party attack the normal form of expression as if they were attacking a statement; the other defend it, as if they were stating facts recognized by every reasonable human being." Definitely not defending any particular position here, but suggesting all parties are mis-using are ordinary language.

From On Certainty(OC)

P. 24, he says, "The idealist's question would be something like: 'What right have I not to doubt the existence of my hands?' (And to that the answer can't be" I know that they exist.). But someone who asks such a question is overlooking the fact that a doubt about existence only works in a language game. Hence, that we should first have to ask: what would such a doubt be like? and don't understand this straight off." Here he is not supporting the skeptical idealist nor the realism of G.E. Moore. Throughout the OC, Wittgenstein is arguing against philosophical skepticism, as well as Moore's Realism, who takes these objective certainties as if they are absolutely unconditional.

So, is Wittgenstein an Idealist or Realist? He is resisting this label because of how he views the purpose of philosophy. Consider the following from PI:

P. 116 "When philosophers use a word - "knowledge", "being", "object", "I", "proposition", "name"- and try to grasp the essence of the thing, one must always ask oneself: is the word ever actually used in this way in the language-game which is its original home? What we do is to bring words back from their metaphysical to their everyday use."

and

P. 124 "Philosophy may in no way interfere with the actual use of language; it can in the end only describe it. For it cannot give it any foundation either. It leaves everything as it is."

Which debate — Banno

Indirect vs direct

I wasn't intending to push Wittgenstein as taking any sides in this rather silly debate. — Banno

I would say Wittgenstein would take neither side of debate.

There's the bad argument again. — Banno

The homunculus surfaces again. At least they can take comfort that they can perceive directly.

For both the Indirect and Direct Realist, there is something in a mind independent external world. The Direct Realist knows that this something is a tree with three branches. The Indirect Realist knows that they perceive a tree with three branches, but doesn't know what this something is in the external world. — RussellA

I believe this distinction is based on perception not knowledge.

The direct realist perceives the tree.
The indirect realist perceives the sense data of the tree.

How does the direct realist know they perceive a tree. Well, there are many actions they could do like look at it from a different angle, touch it, consult an expert, perform a DNA test and so forth.

How about an indirect realist? The same? I feel the pragmatist in me is ready to carve out the metaphysical fat.

I think you will need a stronger argument against Indirect Realism than it is absurd, as, as Searle writes, Direct Realism was not supported by the great geniuses of philosophy. — RussellA

Let me repeat, this is an absurdity derived from a grammatical fiction. What is the fiction? Directly perceived sense data.

Not seeing an answer here. — Banno

Generally, trying to think how these phases are used in everyday circumstances. In my example, using "The tree has three branches", there was no perception of a tree when it was used.

Hoffman would posit that humans have evolved a tailored and limited account of reality which assists us in survival. — Tom Storm

Interestingly, Alvin Plantinga takes this idea to show how evolutionary ideas undermine naturalism. That evolution is only selecting for survival ability and not truth finding ability, thus, our ability to determine the truth of naturalism or anything for that matter is severely questionable.

The question is, when the scientist perceives an event in their laboratory, as Hume asks, can this only ever be an inference ? — RussellA

I think you are saying not only "the scientist perceives an event in their laboratory" as an inference, but "the laboratory" itself can only ever be an inference.

This is an absurdity derived from a grammatical fiction.