I don't really understand what you are asking but I'll try to answer your questions to the best of my ability.

That leaves the question, what is form - assuming the question is meaningful. — tim wood

Form is, as I said, what the thing is. And, since all things have a whatness unique to themselves, it is what individuates one thing from another. It doesn't make much sense to ask what is form because that's like asking what is the form of form. You could ask such a question, but since each form is different from every other form, there cannot be an answer because that would require that all forms are in some way the same. But form is a principle of distinction, not a principle of sameness, while matter is what all material things have in common, so it is the principle of sameness.

As all that is subject to sensation refers back to matter, form cannot be a matter of sensation. Not hard, soft, rough, smooth, hot, cold, etc. But form must be perceived. — tim wood

Form is what is perceived, we perceive differences. Matter is not perceived. We do not perceive sameness, we infer it through reference to memory, 'things have stayed the same', 'the same things are here that were here yesterday', etc.. However, what I was explaining to Wayfarer, is that we do not perceive the entirety of a thing's form, the complete form in its perfections which are proper to it being the thing which its, we perceive an abstracted form. This is why Aristotle has two distinct senses of "form" corresponding with primary and secondary substance. Form is "actual" and Aristotle outlines two very distinct senses of that word.

That leaves a question as to what is in or about matter that lends itself to discrimination due to form. And it would seem to me that whatever it is would lie in the matter itself. — tim wood

Matter is strictly potential, specifically the potential for change. Being the potential for change, it does not itself actually change. Think of concepts like inertia, and the conservation laws of mass and energy. The potential for change does not itself change. In reality, "matter" is purely conceptual, but I believe it refers to something real, something we do not understand, but we know it as temporal continuity. So I think, the fact that many things here in my room today, are the same things which were here yesterday, despite the numerous changes which have occurred in the meantime, is due to their matter. The matter being the potential for change, which does not actually change.

Thus a warm furry kitten is not a red brick, and this difference due to the differences in their matter. — tim wood

Clearly the difference between a kitten and a brick is a difference of form.

I recognize the difficulty in writing clearly and making sense of these matters - at least for me! It seems useful as a first step to recognize that "form" and "matter" are terms of art whose meaning is not to be found in their common English meanings, not least because they're not Greek words. In order to keep mindful of that distinction between the common English and the Greek terms they represent, let's abbreviate them as F and M.

My understanding of Aristotle is informed by a remark in a book, the gist of which is that while modern science tries to improve and refine long existing maps of understanding and knowledge mainly by applying the scientific method, Aristotle had no such maps and no such method. His was dialectical, and his standard was what made sense or could be made or seen to make sense. And with this his was an effort not to refine or improve, but instead to fill large blank spaces in the map of knowledge.

Let's start with this: is M itself material or immaterial? Maybe this way: is M a something or a no-thing? It seems clear it must be a something. As a something it must be intelligible, at least as a something. To say that it is in itself unintelligible can only mean that by itself M is not any particular something. Clay or water or any fluid can stand in as metaphor for M. Taking shape as metaphor for F, it's clear that clay or water or any fluid has no particular shape. But of course clay, water, or any fluid does have its own F, as clay, water, or any fluid. So it seems that M and F must be understood as generalization and abstraction from concrete examples.

F, apparently, is the what-it-is of a particular something. Thus F alone would appear to be simply a descriptive general term for that which every particular F has and is. In other words, no actual particularity, no actual F. It seems reasonable to accommodate this in the abbreviation by changing F to PF.

So far, then, all things known by their admixture of M and PF. And for so long as the urge to translate M and PF into stuff and shape/form, i.e., into modern scientific concepts, is resisted, good. And that is the great problem that swims just below the surface breaching and breaking through the surface, devouring Aristotelian sense.

It is the scientific method against Aristotle's dialectic. In Kantian terms, Aristotle could do no better than to make the world conform to sense, sense being the final arbiter, while modern science tries to make sense conform to the world, the world being final arbiter. And that leaves Aristotle as an historical figure, his ideas enduring either as historical curios or vestigially.

Clearly the difference between a kitten and a brick is a difference of form. — Metaphysician Undercover

In Aristotelian terms, nolo. But as science, inevitably, nonsense.

Let's start with this: is M itself material or immaterial? Maybe this way: is M a something or a no-thing? It seems clear it must be a something. — tim wood

Strictly speaking, matter is potential. What gives it actuality is form. Matter without form, as "prime matter" which Aristotle pondered, is a no-thing, because things have a definite form. In my understanding, Aristotle rejected prime matter as an impossibility, but this is still debated.

To say that it is in itself unintelligible can only mean that by itself M is not any particular something. — tim wood

Yes, that is what Aristotle says. What you call "by itself" is what would be prime matter. Prime matter was proposed by some ancients, as the fundamental stuff which makes up all reality. It could have any form, infinite possibility, and as such, it cannot itself have any form. It's infinite possibility, and that's what makes it unintelligible. He also provided an argument to demonstrate that it is physically impossible.

F, apparently, is the what-it-is of a particular something. Thus F alone would appear to be simply a descriptive general term for that which every particular F has and is. In other words, no actual particularity, no actual F. It seems reasonable to accommodate this in the abbreviation by changing F to PF. — tim wood

I don't quite follow this. But I understand the law of identity as assigning the form directly to the particular, as in the thing itself. That's what Wayfarer seems to disagree with, saying that A was not interested in particulars.

So far, then, all things known by their admixture of M and PF. And for so long as the urge to translate M and PF into stuff and shape/form, i.e., into modern scientific concepts, is resisted, good. And that is the great problem that swims just below the surface breaching and breaking through the surface, devouring Aristotelian sense.

It is the scientific method against Aristotle's dialectic. In Kantian terms, Aristotle could do no better than to make the world conform to sense, sense being the final arbiter, while modern science tries to make sense conform to the world, the world being final arbiter. And that leaves Aristotle as an historical figure, his ideas enduring either as historical curios or vestigially. — tim wood

I don't follow this at all.

Strictly speaking, matter is potential. What gives it actuality is form. Matter without form, as "prime matter" which Aristotle pondered, is a no-thing, — Metaphysician Undercover

Is M just an aspect of F? It seems that M absent F is a no-thing, because were it a thing, it would have F. But if M a no-thing, a nothing, a not anything, and not just an aspect of F, then, not being, how can it be? It apparently has by itself no substance and no predicates. As such, any proposition of the form M is x is nonsense on its face. Yes? No?

F without M seems also nonsensical. The distinguishing characteristic of both M and F would then be particularity. They require a particular something in which to be. But if every-thing is simply an instantiation of M and F necessarily together, than what does "is" mean? Where does being come from; what is being? And if M and F exhaustive of the constituents of everything, being cannot be a part of any thing. That leaves being itself as a predicate, which as such is only in the mind of the one predicating - a product purely of that mind, an idea and apparently useful fiction.

Where am I going wrong here?

That is, even reading here,
https://plato.stanford.edu/entries/form-matter/
it seems that none of these concepts is problem-free. Which is to say they don't actually work. Which throws us back to what I call the dialectic of Aristotle's method. And the science of the matter, in modern terms, cannot accept dialectic demonstration by itself - because it is unreliable and in many cases indemonstrable or even plain wrong.

It seems that M absent F is a no-thing, because were it a thing, it would have F. But if M a no-thing, a nothing, a not anything, and not just an aspect of F, then, not being, how can it be? It apparently has by itself no substance and no predicates. As such, any proposition of the form M is x is nonsense on its face. Yes? No? — tim wood

That's right, withot form, matter would be a no-thing, pure potential. As potential, it neither is nor is not. That's what we were discussing earlier, whether possibility, under the Aristotelian conception, violates the law of excluded middle. This I argue, is what makes it unintelligible.

F without M seems also nonsensical. The distinguishing characteristic of both M and F would then be particularity. They require a particular something in which to be. But if every-thing is simply an instantiation of M and F necessarily together, than what does "is" mean? Where does being come from; what is being? And if M and F exhaustive of the constituents of everything, being cannot be a part of any thing. That leaves being itself as a predicate, which as such is only in the mind of the one predicating - a product purely of that mind, an idea and apparently useful fiction. — tim wood

I don't see how any of this is irrelevant. But form without matter is not left as nonsensical, because form is demonstrated to be prior to matter as cause of a material thing being the thing which it is. Matter is not necessary for particularity, as the essence of a thing is its form. This is what allows for the immaterial forms of Christian metaphysics. That the particulars appear to us as composed of matter and form, does not necessitate that they are not caused by independent forms, prior to material being.

it seems that none of these concepts is problem-free. Which is to say they don't actually work. — tim wood

Having problems is not the same as not working. Human knowledge and understanding will likely never obtain the level of perfection. That implies that even though the things we do have problems, they still work for us. We live with problems. One issue which Aquinas took up. is that because the human intellect is united. and dependent on matter, its ability to understand forms will always be impaired.

I believe in a hard version of the PSR: everything must have a reason/explanation/ground. No exception; not for the fundamental laws of nature or for the PSR itself.

The fundamental laws of nature do not exist necessarily and so must have an external reason to exist.
The PSR has an internal reason to exist (reason type 3). As defended in this post, the PSR is a principle of metaphysics which means it is part of the fabric of reality. And the statement "a thing that is part of the fabric of reality exists" is a tautology and is therefore necessarily true.

This [purpose] is automatically true if you presuppose PSR. This should be true for all types, not necessarily requiring a free-will system. — PartialFanatic

A thing that exists or occurs out of necessity (reasons type 1 and 3) do not need a purpose to explain why they exist or occur. E.g., a water stream looks for the path of least resistance, not purposely but simply out of causal necessity from the laws of nature such as gravity and friction.

In addition, I feel there is a lack of distinction between existential reason (reason for existence) and purpose (reason to exist) in "Man itself" section, although I feel that it is irrelevant to the core argument. — PartialFanatic

I believe these are the same as what is described in the OP as efficient cause and final cause. Indeed, if man is designed, then they would have a reason for existence (efficient cause) as well as a reason to exist (final cause). They would also have the other two causes: material cause (a physical body) and formal cause (a design).

My understanding is that modal collapse or necessitarianism is not strictly speaking impossible, but it is undesirable because it leads to absurd conclusions. It trivializes modal reasoning, and modal logic would be reduced to only very specific applications that would not be metaphysically true. As such, necessitarianism is best to be avoided if possible.

There are no absurd conclusions at all. It doesn't trivialize modal reasoning, because we can still conceptualize how things might have been in counterfactual conditions. We all make use of this, learn from it. "If I hadn't done X then Y (an unfortunate consequence) would not have occurred." Lesson: in the future, avoid doing X.

Concieiving this way doesn't imply that X was metaphysically contingent. Consider why you made decision to do X. If it was an impulse, then something led to the impulse (e.g. the scent of freshly baked cookies induced an impulse to eat one). If X was a deliberative decision, it was consequence of the factors that came to mind. that you weighed in a certain way. There's no obvious source of contingency, so why believe it was actually contingent? Conceivability can lead to modal illusion.

So I don't think it's reasonable to ever assume contingency, unless one can point to a source of contingency.

After doing a bit of research, it seems that modal collapse or necessitarianism is problematic because it removes the freedom that seems intuitive in metaphysics, possible outcomes, decision-making, responsibility, etc. Let's take your example:

"If I hadn't done X then Y (an unfortunate consequence) would not have occurred. Lesson: in the future, avoid doing X."
The underlined sentence is a prescriptive statement, a "should", which implies a freedom to do X or not. If all prescriptive statements were going to occur necessarily, then the prescription is merely an illusion. "I should" becomes "I will (or not)". Why make an effort to learn, grow, or improve if the future is fixed?

So even though we can conceptualize how things might have been in counterfactual conditions, I dispute that this would have any use, even for future cases.

The underlined sentence is a prescriptive statement, a "should", which implies a freedom to do X or not. If all prescriptive statements were going to occur necessarily, then the prescription is merely an illusion — A Christian Philosophy

If I decide not eat cookies (a "should"), this decision establishes a disposition- a factor that will influence, but not necessitate, my future behavior. The craving induced by the scent may create a disposition that may be stronger. The prior disposition is not an illusion, it was simply ignored and the impulse acted on.

I accept compatibilism- an account of free will that is consistent with determinism. It does not entail fatalism. Fatalism is the view that you have no real choices. Compatibilism is the view that our choices are under our control. Choices are the product of internal factors: knowledge, beliefs, desires, wishes, genetic predispositions, learned conditioned responses, dispositions, impulses, mood...

These factors were all caused, but they are bundled uniquely into each of us. They are what make us who we are.

Under compatibilism, we can still entertain past possibilities - the things one might have done, but it correctly recognizes that something would have had to be different: some missing bit of knowledge, improved impulse control. I don't see that libertarian free will can do any more: decisions are still based on reasons. And new experiences and knowledge change us, so that our future decisions will be made on a different basis.

I understand your view of compatibilism but I don't understand why this does not entail fatalism. If all choices are the product of factors (internal or external) and all these factors are caused by something else, then all our choices are caused by something else. Given a specific set of factors, all originating outside of ourselves, the outcome is inevitable.

I don't see that libertarian free will can do any more: decisions are still based on reasons. — Relativist

In other words, you are asking how libertarian free will could be compatible with the PSR.
Libertarian free will is defined as: "the ability to choose without being compelled by external factors (meaning factors other than our will)". Since the "ability to choose freely" is contained in the definition of libertarian free will, then the explanation for our free choice exists inherently in the power of free will (reason type 3 in the OP).

Another way to say the same thing: if we suppose that we have the power of libertarian free will, then how do we explain our ability to choose without being compelled by external factors? Answer: because we have the power of free will; that's precisely what the power is supposed to do.

More details are provided in the following video: https://youtu.be/k_PoOKDVUdc
The full video is 21 minutes long, but you can skip to timestamp 15:28 for this specific topic.

I don't see that libertarian free will can do any more: decisions are still based on reasons.
— Relativist
In other words, you are asking how libertarian free will could be compatible with the PSR. — A Christian Philosophy

No. I'm pointing out that because decision making is consistent with determinism (and thus, the PSR)- there is no basis for insisting we have libertarian free will. You choose to believe we have it, but I do not accept that as a premise.

I understand your view of compatibilism but I don't understand why this does not entail fatalism. If all choices are the product of factors (internal or external) and all these factors are caused by something else, then all our choices are caused by something else. — A Christian Philosophy

Here's the logic you may be applying:

Assume A causes B, and B causes C, then:
A causes C (the logic is transitive)- Implying B is irrelevant. This is a fatalist view.

My point is that B is not irrelevant. Logic is transitive, but causation is not. Our acts of will are "B", and the mental processing that we perform is essential for C to occur.

Compare this to a computer: input- processing- output. The processing is a necessary step - essential to producing the output. "A" consists of the physical parts of the computer, the software, electricity running through the circuits, and the specific input it was given. All those components are essential to producing the output ("C").

I'm pointing out that because decision making is consistent with determinism (and thus, the PSR)- there is no basis for insisting we have libertarian free will. — Relativist

Sure. I accept the burden of proof to defend the existence of libertarian free will. For now, I'll continue to argue that compatibilist free will leads to fatalism.

Our acts of will are "B", and the mental processing that we perform is essential for C to occur. — Relativist

B is essential for C to occur, but this does not dismiss fatalism. E.g. cog A is connected to cog B which is connected to cog C. Cog B is essential for cog C to spin, but cog B has no control over the outcome. Adding complexity to the system, like a computer process or a compatibilist mental process, does not change the fact that there is no control from any of the parts.

B is essential for C to occur, but this does not dismiss fatalism. E.g. cog A is connected to cog B which is connected to cog C. Cog B is essential for cog C to spin, but cog B has no control over the outcome. — A Christian Philosophy

Two problems with this:
1. We have agency:
- the capacity to act intentionally
-the capacity to initiate action
-we reflect on, and care about, our actions

2. Fatalism entails an attitude of futility in the face of future events. If you're sick, your recovery (or death) is fated to occur - and this will occur regardless of whether or not you seek medical care. This is obviously not the case: we typically choose to act a certain way in order to achieve a desireable outcome. We choose medical care because we anticipate that it will improve our chances of recovery.

I agree that we have real agency, and yet this is not possible under necessitarianism where all actions from every part, like cogs, are necessary.

I agree that fatalism is a wrong view, and yet under necessitarianism, we have no power over future events since the future is fixed.

I agree that we have real agency, and yet this is not possible under necessitarianism where all actions from every part, like cogs, are necessary. — A Christian Philosophy

Assertion without argument. You refuted none of the 3 aspects of agency I identified:
-the capacity to act intentionally
-the capacity to initiate action
-we reflect on, and care about, our actions

I agree that fatalism is a wrong view, and yet under necessitarianism, we have no power over future events since the future is fixed. — A Christian Philosophy

You're ignoring everything I said. If you're very sick, you choose to seek medical care because you believe it improves your chances of recovery. If you lacked that belief, you wouldn't bother. A fatalist wouldn't bother, because he assumes his outcome is fated to occur and any actions he takes are futile.

Compatilists refer to the "principle of alternate future possibilities" - the set of choices before us. I am free to make a choice among options before me. This is distinguished from the "principle of alternate possibilities" (implying past choices were contingent) that most incompatibilists consider essential to libertarian free will. This principle implies that our past choices could have differed from what they were.

A compatibilist, like me, recognizes that our actions influence the future, and so we make choices accordingly. In one sense, past choices could have been different - but only if there were something different, like a different (or stronger) belief.

Your choices seem free to you, I'm sure. You agreed the decision process is consistent with the PSR, so exactly what can you show to be inconsistent with determinism?