In defence of the Principle of Sufficient Reason

A Christian Philosophy

Introduction
Principle of Sufficient Reason (PSR): For any thing that exists or is true, there is a sufficient reason for it to exist or to be true.

The PSR is a first principle of both metaphysics (the science of fundamental reality) and epistemology (the science of validation of knowledge), alongside the other first principle: Logic. Until the beginning of the 20th century, the PSR was referred to as “the fourth law of thought”, coming after the three laws of logic. The PSR started to go out of vogue in the 20th century, likely due to the rise of quantum physics that challenged the principle (details further down).

In this post, we describe the principle in the context of epistemology and metaphysics, and its parallel with logic. We then defend its validity as a first principle and against the challenge of quantum physics.

PSR in Epistemology
• In the context of epistemology, the PSR states: “For every claim that is true, there is a sufficient reason for it to be true.”
• In this way, the PSR is also called “Principle of Parsimony” or “Occam’s Razor”: the simplest explanation that accounts for all the data is the most reasonable one.
• E.g. Say we observe something that looks like a duck, acts like a duck, and sounds like a duck. We posit three explanations:

(1) It’s a robot remotely controlled by the government to seek out communist partisans.
(2) It’s nothing.
(3) It’s a duck.

• All three explanations are logically possible, but explanation (1) is more than sufficient or superfluous, and explanation (2) is less than sufficient. Explanation (3) is the simplest one that accounts for all the data; and is therefore the most reasonable one.

PSR in Metaphysics
• In the context of metaphysics, the PSR states: “For every thing that exists, there is a sufficient reason for it to exist.”
• The type of sufficient reason that fulfills the PSR can be divided in 3 ways:

1. Internal reason: The existence of a thing is explained by logical necessity or inherently. E.g. The outcome “4” exists from “2+2” by logical necessity. The property of “3 sides” exists in all triangles inherently.
2. External necessary reason: The existence of a thing is explained by causal necessity. E.g. a rock falls to the ground when dropped. The fall is explained by causal necessity due to laws of physics.
3. External contingent reason: This only applies to beings with free will. The existence of a thing or action is explained by a free choice that is motivated by an end goal. E.g. In the morning, a person has the free choice to stay in bed under the motive of staying comfortable, or to get up and go to work under the motive of making money.

Relation between the PSR and Logic
Both the PSR and logic are first principles of metaphysics and epistemology. The two principles are independent, i.e. the PSR cannot be derived from logic and logic cannot be derived from the PSR; however, parallels can be drawn between the two.

In epistemology:
• Logic is associated with deductive reasoning. E.g. saying “4 is deduced from 2+2” is equivalent to saying “4 logically follows from 2+2”.
• The PSR is associated with inductive reasoning. E.g. saying “From observing that each particular swan is white, we induce that all swans are white” is equivalent to saying “The claim that all swans are white is the most sufficient explanation for why we observe that all swans are white”.

In metaphysics:
• Logic rules over the realm of possible worlds:

E.g. a 4-sided triangle is not logically possible, i.e. it exists in no possible world.
Horses and unicorns are logically possible, i.e. they exist in some possible world.
But logic alone cannot tell us that horses and unicorns exist in the actual world. Even after we observe horses in the world, it is still logically possible that we have a false perception.

• The PSR rules over the realm of the actual world (complemented by observation):

E.g. After we observe horses in the world; we posit that horses exist in the actual world because this is the most sufficient explanation.
On the other hand, we posit that unicorns do not exist in the actual world because we don’t have a sufficient reason to believe they exist.

In the sciences:
• All sciences are founded on logic, and most sciences are also founded on the PSR because they refer to real things in the actual world, and because they aim to seek reasons, causes, and explanations for observed events.
• Only two sciences are founded on logic alone: formal logic and mathematics (which is logic applied to numbers). We also note that those two sciences are empty of actual objects. E.g. in the syllogism “if A=B and B=C, then A=C”; the variables A, B, and C are empty.

Now that we have described the PSR, let’s defend it as a principle.

Argument in defence of the PSR
1. We start with the proposition “Reason finds truth." This proposition is self-evident because any reasoning for or against it presupposes that our reasoning process finds truth. And yet, everyone believes this proposition to be true because everyone uses reason to find truth. Also, planes fly :)
2. We observe that our reasoning works in 2 ways: deduction and induction (and abduction is not really different from induction).
3. As shown above, deduction is equivalent to the principle (or laws) of logic, and induction is equivalent to the principle of sufficient reason.
4. Thus, the PSR is a first principle of epistemology, alongside logic.

5. Now, truth means "conformance to reality". E.g. the proposition “the earth is round” is true only if the earth is round in reality.
6. Thus, if reason is able to find truth, it must be because its process imitates the behaviour of reality. I.e. If we know the initial conditions A, we can infer conclusion B using our reason. This reasoning is true only if conditions A result in outcome B in reality.

Example for logic: If we have 2 spoons and add another 2 spoons, we predict by our reason that we will have 4 spoons. And indeed, this outcome occurs in reality.
Example for the PSR: If we observe the existence of an egg, we infer the prior existence of a cause as a sufficient reason, like a chicken. And indeed, we verify that all chicken eggs come from chickens in reality.

7. Therefore, logic and the PSR are not only principles of epistemology but also principles of metaphysics.

It is correct to think logically because reality behaves logically. If it wasn’t the case, there would be no reason to think logically.
It is correct to look for reasons to things because reasons exist in reality. If it wasn’t the case, there would be no reason to find sufficient reasons.

Counter-Argument against the PSR: Quantum Physics
Argument: According to quantum physics, the behaviour of some particles is random, that is, they behave a particular way without reason, with no hidden cause. Since the PRS demands a sufficient reason for everything that exists, including a behaviour, then this phenomenon runs against the PSR.

Response: Our response is in two parts. First, we show that quantum physics cannot go against the PSR; and second, we show that the phenomenon is in fact compatible with the PSR.
Part 1. Quantum physics cannot refute the PSR:

1. Quantum physics is a branch of physics, which is an empirical science.
2. And all sciences except for formal logic and mathematics are in part founded on the PSR (as shown above). I.e. quantum physics demands some observations, and rely on the PSR to make claims about reality.
3. As such, if quantum physics were to refute the PSR, then it would refute itself, like a tree cutting off its own roots.
4. Therefore, quantum physics cannot refute the PSR.

Part 2. The behaviour of quantum particles is compatible with the PSR:

1. Nevertheless, the fact remains that physicists claim that some particles behave randomly with no hidden cause.
2. We can accept this claim if we understand that “no hidden cause” implies “no physical hidden cause”. Physicists are experts in physics, not metaphysics, and thus their authority does not extend past the field of physics.
3. Unless we can defend the claim that “all that exists is physical”, a claim which falls outside the authority of physicists, then nothing prevents particles to have a non-physical cause. For philosophers, this claim is usually defended by appealing to Occam’s Razor which is another name for the PSR. As such, appealing to the claim that “all that exists is physical” to refute the PSR is self-refuting.
4. With that, we preserve the claim that “quantum particles behave a particular way with no hidden cause” in the field of physics, and the PSR is preserved in the field of metaphysics. Note: we are not aiming to solve some quantum problem here, but merely showing that possible solutions exist that reconcile quantum physics with the PSR.
5. Therefore, the behaviour of quantum particles is compatible with the PSR.

Questions, comments, objections?
Note: I am NOT an expert in quantum physics at all, so when discussing quantum, please keep it surface level and use layman terms for my sake. Much appreciated! :)

RussellA

Counter-Argument against the PSR: Quantum Physics — A Christian Philosophy

In addition, something that nobody understands cannot properly be used as a counter-argument against anything.

As Feynman said "I think I can safely say that nobody understands quantum mechanics"

ssu

In my view @RussellA has a point. Why link Quantum Mechanics with something that is on a basic theoretical level? You'll easily simply drift to a debate about QM.

Isn't here already the existence of randomness enough? In many instances the best model of reality is randomness or stochastic processes. Throw of a dice. This isn't an obstacle for determinism, because if you throw a dice, you will get a dice number. Yet the process is easily and efficiently modeled as the dice number being random (from 1 to 6, if the dice is a cube).

Is this an obstacle to PSR? In my view no. I would argue that it is PSR, sufficient reasoning.

Anyway, when trying to measure something or the observation itself affects what is tried to be measured or observed, you cannot have total objectivity. The measurer plays a part in what happens. And as we are part of the universe, we simply cannot assume objectivity of us not being part of the universe. We cannot look at the university from outside it.

Again, is this a counterargument for PSR? No.

tim wood

↪A Christian Philosophy

Heidegger wrote a book, The Principle of Reason. It starts,
"The principle of reason reads: nihil est sine ratione. One translates it: nothing is without a reason" (3). And then on for about 130 pages. What I get from it, and him, is that the "reason" is the story of the moment that best accounts for "why the matter has run its course this way rather then that" (119).

That is, as I understand it, given that there are things of all sorts, there is no such thing as a reason. And therefore it follows that it is a very great, fundamental, and ignorant mistake to look for any such thing. But a story, on the other hand, if it's a good story, establishes its own value by itself - and if of sufficient value, becomes regarded as a thing.

Of course, for good stories to become "things," other stories, usually, must have always already been regarded as things, like "reality" and "truth" and "logic," and others as well. Nothing wrong with this; it's the way the world works - denial a short road to madness. But sometimes it is important to remember that it is all a story, and perhaps the moral of the story being that all is contingent and provisional and that we can have practical knowledge and practical truth, but always within the context of the ground of a story, and nothing absolute.

Heidegger: "Accordingly, humans are the animal rationale, the creature that requires accounts and gives accounts," (129). He then asks if this determination "exhausts the essence of humanity?" (129). A good question, and the book worth the read.

RussellA

For any thing that exists or is true, there is a sufficient reason for it to exist or to be true.............................We observe that our reasoning works in 2 ways: deduction and induction — A Christian Philosophy

The Principle of Sufficient Reason (PSR) proposes that for every fact F, there must be a sufficient reason why F is the case (SEP - Principle of Sufficient Reason)

We use deduction and induction when reasoning.

Hume's critique of causation challenges PSR. In his Treatise of Human Nature, Hume considers the idea that whatever begins to exist must have a cause, but he finds this open to doubt. Since cause and effect are distinct, one can imagine an event without a cause. Hume said that induction gives truth only if nature is uniform, and if we do use induction, we are presupposing the uniformity of nature, which may or may not be the case (SEP - Principle of Sufficient Reason).

However, this introduces an inevitable circularity as induction and deduction presuppose a uniformity in nature, which may or may not be the case. Therefore any reason we come up with for a fact based on induction and deduction may or may not be the case.

It follows that given a fact, as we can never know whether any particular reason is or is not the case, we can never know whether for any fact there is a reason or not.

We could only say that for every fact there must be a sufficient reason why F is the case if we knew that nature was uniform. But we don't know that nature is uniform. We know that many aspects of nature are contingently uniform, but we don't know that they are necessarily uniform.

jgill

mathematics (which is logic applied to numbers). — A Christian Philosophy

Overly simplistic IMO. Although mathematical proofs are applications of logic.

A Christian Philosophy

↪RussellA

Yes I agree. When responding to quantum physics objections, I think I'll use your response first before trying a more elaborate argument like in the OP. Thanks!

A Christian Philosophy

Isn't here already the existence of randomness enough? [...] Throw of a dice. This isn't an obstacle for determinism, because if you throw a dice, you will get a dice number. Yet the process is easily and efficiently modeled as the dice number being random (from 1 to 6, if the dice is a cube). — ssu

I know you said this does not refute the PSR; however, I want to clarify that statistical randomness like throwing a dice is not real or metaphysical randomness. We call the outcome of throwing a dice random because we are not fully in control of the outcome; however it is not truly random because it is only a bunch of forces acting on the dice, all of which are determined. I.e., if we were to throw a dice the exact same way every time, then the same outcome would result every time.

A Christian Philosophy

↪tim wood

Thanks for sharing! Interesting stuff.

A Christian Philosophy

↪RussellA

Good point.
I think what you are trying to say is we cannot know with certainty that nature is uniform, that the future will resemble the past. I agree, but I don't see it as an issue in practice: (1) Most people would agree that our reason is a reliable tool to find truth, and our reason uses induction. (2) It has been the case so far that nature is uniform - planes fly pretty well. Thus, while the uniformity of nature is not known with certainty, it is still known beyond reasonable doubt.

one can imagine an event without a cause. — RussellA

This is expected because the test of imagination is associated with logic, and the PSR (which includes causality) is not derived from logic.

A Christian Philosophy

↪jgill

Yeah probably. Out of curiosity, would you have a better description of mathematics?

Clearbury

↪A Christian Philosophy

I do not see why the principle of sufficient reason is equivalent to the principle of parsimony. They seem like two quite different principles. The first says that for anything that exists, there is an explanation of its existence (the word 'reason' in 'principle of sufficient reason' refers to an explanatory reason). The principle of parsimony says that for any two or more possible explanations, we have reason to think the simpler one is true, other things being equal. The word 'reason' in the principle of parsimony refers to a justifying reason. These are not the same principle at all, I think.

I also do not see why accepting the truth of the principle of sufficient reason is required to be able to engage in intellectual inquiry. For example, imagine I think it is false for I think that if it is true, then some things must explain themselves (for not everything can have a cause external to it - as that generates a regress - and nothing can be the cause of itself, as that's a contradiction). As nothing can explain itself, I conclude that some things exist and have no cause of their existence (and thus that the principle of sufficient reason is false).

Why does denying the principle of reason - as I have just done - preclude me from using my reason to find out what is true? I think our reason is our source - our only source - of insight into the nature of reality. And it was by using it - perhaps incompetently, admittedly - that I arrived at the conclusion that the principle of sufficient reason is not a true principle of reason at all, but contrary to reason. I do not see, then, why rejection of the principle of sufficient reason undermines the project of using reason to find truth. For all I have concluded - and concluded by using my reason - is that some existences do not have explanations. I have not concluded that nothing has an explanation. And i have not rejected the principle of parsimony either, for i plan on using it to try and find out which existences are the ones that lack explanations.

jgill

↪jgill
Yeah probably. Out of curiosity, would you have a better description of mathematics? — A Christian Philosophy

As a former prof I never gave much thought to a definition. But this is OK.

RussellA

Thus, while the uniformity of nature is not known with certainty, it is still known beyond reasonable doubt. — A Christian Philosophy

From the SEP article Principle of Sufficient Reason: the PSR may be formulated as "For every fact F, there must be a sufficient reason why F is the case."

I agree that although the uniformity of nature is not known with certainty, it is still known beyond reasonable doubt.

Does this mean that the PSR should be re-formulated as "For every fact F, there is probably a sufficient reason why F is the case."
===============================================================================

one can imagine an event without a cause...............This is expected because the test of imagination is associated with logic, and the PSR (which includes causality) is not derived from logic. — A Christian Philosophy

In other words:
P1 - We can imagine a fact/event
P2 - The test of imagination is associated with logic
P3 - The PSR states that given a fact/event there must be a reason/cause
P4 - The PSR is not derived from logic
C1 - We can imagine a fact/event that doesn't have a reason/cause

In particular:
P1 - We can imagine a unicorn
P2 - We can test that the unicorn we imagine is true or not using logic.

P1 - I imagine a unicorn in my mind
P2 - I have never seen a unicorn in the world
C1 - Therefore, it is possible that unicorns only exist in my mind
C2 - Therefore, it is possible that unicorns may or may not exist in the world.

P3 - True
P4 - Depends what is meant by "derived"
In logic, conclusions follow from premises based on the structure of arguments alone, independent of their topic and content. (Wikipedia - Logic).
An attempt may be made to prove the PSR using logic

P1 - If there can be a fact/event without a reason/cause, then the fact/event could have been other than it is.
P2 - By the Law of Non-Contradiction, a fact/event cannot be other than it is
C1 - Therefore, a fact/event must have a reason/cause

The PSR may possibly be proved using logic, even though there is no logical necessity that a fact/event has a reason/cause.
C1 - We can imagine a unicorn in our mind even if unicorns don't exist in the world.

We can imagine a unicorn in our mind even though there is no unicorn in the world. Does this mean that there is nothing that has caused us to imagine a unicorn in our mind?

ssu

↪A Christian Philosophy

The point is that metaphysical randomness wouldn't refute PSR. There are so many events where simple probability theory /probability calculus works well. It is a sufficient way to model reality, just as game theory is.

My point was that you don't have to refer to Quantum Physics as the reason for this. The measurement problem happens even without Quantum Physics. This basically comes from the fact that we ourselves are part of the universe ourselves.

Philosophim

A few things to add to this:

Reason is simply identifying something logically. A leads to be, or A sometimes leads to B for example. Sufficient reason is that there is a logical descriptor that correctly identifies what is true.

In other words, what exists, exists. Reason is the way we interpret that existence in a way that fits in with a logical framework. As an example: The big bang appeared from nothing. If that is true, then the sufficient reason for that happening is simply a logical framework that accurately leads to this result.

In other words: Everything can be sufficiently reasoned to if one knows what is true. This is purely through the invention of a human framework that can result in the correct conclusion. The mistake is thinking that if one has created a framework that leads to a conclusion through reason alone, that this necessarily makes the conclusion true. Truth must exist first for reason to matter.

Fooloso4

“For every thing that exists, there is a sufficient reason for it to exist.” — A Christian Philosophy

What is the reason for existence?

What is the reason for thinking that there must be a reason for what is?

Count Timothy von Icarus

I'll just share Kenneth Gallagher's metaphysical (as opposed to nomic/physical necessity) principle of causation vis-a-vis mobile being:

For no being insofar as it is changing is its own ground of being. Every state of a changing being is contingent: it was not a moment ago and will not be a moment from now. Therefore the grasping of a being as changing is the grasping of it as not intelligible in itself-as essentially referred to something other than itself.

Kenneth Gallagher - The Philosophy of Knowledge

LuckyR

The outcome “4” exists from “2+2” by logical necessity

↪A Christian Philosophy

While true, it is bordering on insignificant and useless. Basically you're saying if you give me an answer I can come up with an equation that comes up with that answer. Of course my equation may not be how Nature came up with that answer, but it's AN equation that explains the answer. BTW, many, many actual explanations don't initially seem to be the most reasonable explanation.

Basically a bundle of (next to) nothing.

T Clark

In other words, what exists, exists. Reason is the way we interpret that existence in a way that fits in with a logical framework. As an example: The big bang appeared from nothing. If that is true, then the sufficient reason for that happening is simply a logical framework that accurately leads to this result. — Philosophim

I like this. I think it's a useful way of looking at the issue. I hadn't thought of it in these terms before.

Truth must exist first for reason to matter. — Philosophim

Hmmm... I wonder if I agree with this.

Philosophim

I like this. I think it's a useful way of looking at the issue. I hadn't thought of it in these terms before. — T Clark

Thank you, I'm glad its something new to think about.

Truth must exist first for reason to matter.
— Philosophim

Hmmm... I wonder if I agree with this. — T Clark

That statement only makes sense in relation to the sentence prior.

The mistake is thinking that if one has created a framework that leads to a conclusion through reason alone, that this necessarily makes the conclusion true. Truth must exist first for reason to matter. — Philosophim

We can come to reasonable conclusions that are not true, and that was all that was intended by that last sentence. There is of course value alone in reason even if it does not sometimes lead to the truth, as reason is our best tool to find out what actually is true. But if there were no truth that we were actually mulling on, such reason would be no more useful than a flight of fancy.

Wayfarer

↪Count Timothy von Icarus

'Being' is a verb. Often overlooked.

Wayfarer

What is the reason for thinking that there must be a reason for what is? — Fooloso4

In Greek philosophy, wasn't that simply a presumption that the world was governed by reason? A kind of intuitive sense that there is a reason for everything as well as every thing - one of the meanings of 'logos' from which we derive logic, and all the other -logies. I don't think it dawned on any philosopher, before the advent of modernity, that the Cosmos - a word meaning 'an ordered whole' - could be anything other than rational. Of course the scientific revolution introduces a wholly different conception of reason as mechanical causation. With the banishing of teleological reasoning the idea of reason in that classical sense fell out of favour.

In the pre-modern vision of things, the cosmos had been seen as an inherently purposive structure of diverse but integrally inseparable rational relations — for instance, the Aristotelian aitia, which are conventionally translated as “causes,” but which are nothing like the uniform material “causes” of the mechanistic philosophy. And so the natural order was seen as a reality already akin to intellect. Hence the mind, rather than an anomalous tenant of an alien universe, was instead the most concentrated and luminous expression of nature’s deepest essence. This is why it could pass with such wanton liberty through the “veil of Isis” and ever deeper into nature’s inner mysteries. — David Bentley Hart

I think the OP, being grounded in Christian philosophy, assumes a similar view. Although it's also interesting that the atheist Schopenhauer grounded his entire philosophy on the 'fourfold root of sufficient reason' and refers to it continually in his writing. Itv was Neitszche who foresaw the sense in which the acid of modernity dissolved the whole idea of cosmic reason.

Count Timothy von Icarus

↪Wayfarer

Yes, the "intellect as a whole" as the image of the cosmos versus "the mathematical model."

A Christian Philosophy

I do not see why the principle of sufficient reason is equivalent to the principle of parsimony. They seem like two quite different principles. [...] — Clearbury

They are still the same. In the principle of parsimony, it is reasonable to pick the simplest of 2 explanations that account for all the data because the less simple explanation is superfluous, that is, more than sufficient. Both principles demand that the explanation or reason be just sufficient, not more, not less.

For example, imagine I think it is false for I think that if it is true, then some things must explain themselves (for not everything can have a cause external to it - as that generates a regress - and nothing can be the cause of itself, as that's a contradiction). As nothing can explain itself, I conclude that some things exist and have no cause of their existence (and thus that the principle of sufficient reason is false). — Clearbury

I agree that a thing cannot be its own cause, yet a thing can explain itself. A cause is not the only way to explain the existence of a thing, as described in the OP under the section "PSR in Metaphysics". Another way is that the existence of a thing is explained inherently or by its own definition. I.e. if a thing possesses existence as an essential property, then its existence would be explained inherently or by its own definition. And this would fulfill the PSR.

A Christian Philosophy

↪jgill

Thanks!

A Christian Philosophy

P1 - If there can be a fact/event without a reason/cause, then the fact/event could have been other than it is.
P2 - By the Law of Non-Contradiction, a fact/event cannot be other than it is
C1 - Therefore, a fact/event must have a reason/cause

I dispute P2. By the Law of Non-Contradiction, a fact/event cannot be other than it is at the same time.
Suppose true randomness exists such that event 1 occurs without reason. Still, by the law of non-contradiction, event 1 cannot be something else at the same time. But it still occurred without reason.

We can imagine a unicorn in our mind even though there is no unicorn in the world. Does this mean that there is nothing that has caused us to imagine a unicorn in our mind? — RussellA

I believe that something has caused us to imagine a unicorn in our mind. Something like the experience of having seen horses and horns in the world, and we put them together in our mind.

A Christian Philosophy

↪ssu

Ah, gotcha.

RussellA

By the Law of Non-Contradiction, a fact/event cannot be other than it is at the same time.
Suppose true randomness exists such that event 1 occurs without reason. Still, by the law of non-contradiction, event 1 cannot be something else at the same time. But it still occurred without reason. — A Christian Philosophy

I agree that by the Law of Contradiction, a fact/event cannot be other than it is at the same time. For a fact to be other than it is at the same time is a contradiction in terms. For example, the fact that apple A is on the table is a different fact to the fact that apple A is on the floor.

P1 - Let there be an event which could be either event 1 or event 2, where event 1 and event 2 are different.
P2 - The Principle of Sufficient Reason states that if event 1 occurs there must be a reason.
P3 - By the Law of Non-Contradiction, if event 1 occurs then event 2 could not have occurred.
P4- Suppose event 1 occurs without reason.

C1 - From P4, if event 1 occurs then event 2 could have occurred.
C2 - C1 and P3 are contradictory.
C3 - Therefore, if the Law of Non-Contradiction is valid (P3), then events occurring without reason is invalid (P4).

ssu

↪A Christian Philosophy

Great! Somebody understood me. :smile:

Suppose true randomness exists such that event 1 occurs without reason. — A Christian Philosophy

I wouldn't say this.

Randomness doesn't meant that there isn't any reason. Randomness simply means that there isn't any self repeating pattern or patterns to be found. That there is no pattern doesn't make reason to disappear, what it means that the only correct model is the patternless entity itself. You cannot perfectly model in it a shorter way, like saying that there's an algorithm that can explain it shorter. Basically this idea comes from Algorithmic Information Theory.

Fooloso4

I don't think it dawned on any philosopher, before the advent of modernity, that the Cosmos - a word meaning 'an ordered whole' - could be anything other than rational. — Wayfarer

For Heraclitus the tension of opposites is essential. We may think of it is the function of reason to disambiguate, but logos holds opposites together in their tension. Logos does not resolve all things to 'is' or 'is not'.

Men do not know how what is at variance agrees with itself. It is an attunement of opposite tension, like that of the bow and the lyre.

(fragment 51)

We must know that war is common to all and strife is justice, and that all things come into being and pass away through strife.

(fragment 80)

In the Phaedo Socrates says:

One day I heard someone reading, as he said, from a book of Anaxagoras, and saying that it is Mind that directs and is the cause of everything. I was delighted with this cause and it seemed to me good, in a way, that Mind should be the cause of all. I thought that if this were so, the directing Mind would direct everything and arrange each thing in the way that was best. If then one wished to know the cause of each thing, why it comes to be or perishes or exists, one had to find what was the best way for it to be, or to be acted upon, or to act. On these premises then it befitted a man to investigate only, about this and other things, what is best.

(97b-d)

Socrates accepted Mind as the cause, but instead of inquiring about what Mind is, or how it arranged things, he sought an explanation for why it is best that things be the way they are. He did not find such an explanation in Anaxagoras or anywhere else. He thus launched his “second sailing” to find the cause. (99d). With his “second sailing” Socrates looks to what seems best in a double sense. First, he wants to understand how it is best that things are arranged by Mind as they are, and second, having failed to understand things as they are, that is, to attain truth and knowledge, he seeks what seems to be the best argument.

Mind or nous as the governing principle, arranging things according to what is best, is not the same as a world governed by reason.

For Aristotle, the question of the intelligibility of the natural world faces two problems, the arche or source of the whole and tyche or chance. We have no knowledge of the source and what happens by chance or accident does not happen according to reason.

In defence of the Principle of Sufficient Reason

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