On skepticism, sensation & the principle of sufficient reason
PSR is, as Garrigou Lagrange describes, a direct derivation or explanation of our metaphysical concept of being. The PSR states "that which something has, but not according to its essence, is actual in it due to an extrinsic cause". Just a statement that whatever actuality is before us right now in a thing, either is its own or something else's. In this sense PSR is self-evident & convertible with the principle of identity.
But PSR cannot totally assuage skepticism, especially concerning sensory knowledge.
What follows is a repost of my comments on the subject in various conversations over the past week. Nothing is duplicated hereexcept what I have authored myself - Mike@GreenDragonCVR
*On PSR, skepticism & sensation
The principle of sufficient reason cannot guarantee the validity of sense impressions. A priori, there will always be other sufficient reasons for an impression than what initially appears. We may be hallucinating; our impression of ourselves as distinct subjects may be false; we may be in the matrix, be receiving impressions from a separate substance. All these are sufficient reasons for a sense impression.
But, in these scenarios, metaphysical knowledge is still possible. We may be mistaken concerning what kind of being is before us; but in any case it will be a being. Our (intellectual, not sensible) apprehension of being can take flight from any kind of thing & will pertain equally to any other.
All to say, the PSR does guarantee the validity of our apprehension of the object of metaphysics. Being "cannot be diversified by extrinsic differences, which it actually & implicitly includes". Thus the specificities of where we find it are insignificant & any mode of being (even a hallucinatory impression) will be equally suited to the purpose.
So, even with teleology and psr, there will never be the kind of certitude in sensible knowledge you might expect (which we can find in metaphysics); there can always be a different sufficient reason (than the veracity of the impression) for having an impression (like say the involvement of a separate substance).
As for teolology, it comes with our knowledge of being. Teleology can only, in metaphysical terms, be interpreted in terms of act-potency relationality.
Being, we agree, is obvious (we might say "self-evident"; it lacks extrinsic differences. I'll repost below a blurb from a week ago about being & skepticism).
But for being to not be simply one as per parmenidean monism, being (Aristotle & thomism say) must be intrinsically diversified, into potency and act.
Potency is intrinsically relational; thomism calls it a "transcendental relation" to actuality. Unlike relations inherent in something else as an accident, potency simply is a relation to act, in its very essence: "of its notion potency, and this is its intelligibility itself, all the intelligibility it possesses, is reference to a particular act.... the precise meaning of finality is this reference of potency to act" (Maritain in Preface to Metaphysics).
So insofar as we know being, and we know that being isn't simply one, we know (since there is potency) that there is finality in the universe.
The senses are one such potency, with their own proper object (sensible characters of physical things). It's not that they don't have this telos, it's that (in the case of the senses) OTHER THINGS can actuate these potencies (and disrupt the veracity of sense knowledge).
This is not true of metaphysical knowledge (for there can be no "incorrect" sufficient reason for our apprehension of being & God is the only sufficient cause of the being of creatures!)
This is behind the thomistic observation that metaphysics is the most certain knowledge.
* a note on the impossibility of skepticism re being; a thomist response to academic skepticism
A thomist response to skepticism would probably address how the object of metaphysics, being, is not susceptible to "doubt" in the manner of special categories (of being) or contingent things. We can doubt almost every-thing, true, but not the most important things!
Skepticism takes for granted the preponderance of one kind of being over another, be it material, subjective-ideal, whatever. It interrogates how we know other kinds of being exist outside the one kind it posits as fundamental. Thomists say as much but so does Hegel, who observes (in the encyclopedia logic) that skepticism requires a dogmatic one-sidedness which assumes a world of finite determinations which are opposed (& the perceiver locked within one).
Thomas himself already addressed this in responding to arguments posed by the sophists: nothing is known outside thought, but the object of thought is not the knowing subject & is rather identical (in form) with the thing known.
Well & good... but next we might ask "how can we be certain of [the reality of] any particular OBJECT of thought, even granting that object isn't reducible to subjectivity?"
This is where later Thomists flesh out the response to skepticism. We can indeed doubt almost any special mode of being or contingent thing... anything which may have been otherwise, which has an extrinsic difference.
But since metaphysics starts from being (from the intellect intentionally adopting this form), it is strictly not important which special mode of being it starts from: being is "polyvalent, transspecific, transcategorical", the "highest form of all", which actually & implicitly contains all its differences.
So we may doubt there is anything outside our heads. Or even assume we are in the matrix. Or hallucinating.
But from the pov of first philosophy (where I take it skepticism usually stakes its claim), who cares? A hallucination is no less a mode of being than a physical body. Or we can say "the being we find in any-thing actually & implicitly contains all things". This applies equally to any permutation of specific things or events we might imagine.
As such, we may doubt that we exist in this historical moment or within the categories that seem to define us. But "doubting" being is incoherent. We are able to doubt only from the vantage of one thing in relation to differences extrinsic to it; while being is a polyvalent, intrinsically-diverse form, which includes its differences & is not extrinsically diversified.
(& from the existence of any being, we can know the existence of a first cause! In a way God is more knowable to us than ourselves!)
This is rephrased from Lagrange's "God: His Existence & Nature" & Maritain's "Degrees of Knowledge", wherein both treat Thomas's assertion that "we cannot be deceived concerning simple objects".
Note again that Lagrange thinks the difficulty posed by skepticism is not new, was raised by sophists centuries ago, addressed in book 4 of the metaphysics & summa 1.85.2 (where thomas distinguishes between the thing known vs concept as instrument of knowledge).
*act, potency &sufficient reason
Act & potency are the very rationale of PSR; one thing can only be the reason for another inasmuch as first thing is actual in a manner second thing is in potency!
So it makes sense that PSR is not really conceivable apart from the act/potency distinction
Remember though why that distinction is invoked: to account for the multiplicity, change & limitation of creatures. It is before all semantic, logical or derivative metaphysical considerations, as the condition of affirming the reality of many beings!
*a further note on why being cannot be “doubted”
Doubt takes place from the standpoint of one kind of being in relation to others
Thus the idealist says "something outside thought is unthinkable". Skepticism requires "dogmatic one-sidedness that locks the thinker within one difference of being to the exclusion of others".
But being is not extrinsically diversified; it contains its differences. So even if you are mistaken about some particular "layer" of reality, and say happen to be hallucinating instead of walking around outside, in any case "being is there"
*why the act/potency distinction is necessary
It is a question of what diversifies being.
A genus like "animal" can be diversified by extrinsic differences, like "rational".
But outside of being there is nothing.
So for there to be more than simply one global pantheistic being which comprises all things, being must be divided into act & [different 'ratios' or modes of] potential being.
We can parse this any way we like, but it would apply alike to any number of beings, even individually-diverse atoms.
I think we can even adopt a bit of a Heideggerian posture here and say more strongly "everyone is a believer in the act-potency/being-itself-beings distinction".
That is, everyone posits some-thing as fundamentally real, an "ontological primitive"; then they explain all other things as "potencies" or possible ways for the funamental thing to behave or express itself.
My favorite case is Richard Rorty (pictured), who literally says "all reality is Physical [p1], and other things are different kinds of physical being [p2+]". He even indulges in a distinction between "actual and potential states of the physical universe" LOL. The next page he flaunts his supposed aloofness from Aquinas. What a goof.
The only real question is if the "ontological primitive" we choose is adequate to the task. "Being" is, and explicitly so, can account being & difference, the "problem of the one and the many", while no determinate mode of being (like "the physical") can contain its own differences in principle.
*further comments
a) you might consider the composite a middle ground between act and potency, but it is intrinsically still an act-potency composition
b) you can use a different word for it, but *everyone* postulates being (the in-itself) vs its derivative modes
c) intelligibility just is the being of a thing. Insofar as something exists, it is in principle "intelligible", apt to be the form of an intentional act...
However, nothing is close to intelligible to EVERY subject. "Nothing is received except acc to mode of the receiver", Thomas says; given the finite aptitude of my intellect or yours to know, in principle (despite their intrinsic intelligibility), we can see why some things might be unintelligible to us.
A last consideration: the doctrine of act & potency says Lagrange, means that (insofar as potency exists in the universe) we must expect "a relative absence of determination and intelligibility". Inasmuch as all being is knowable, it is knowable as it is actual. While the potency in it is an element of unknowability, inherent in all things but God in the end! We must accept this as a condition of being a creature (some "irrationality" if you will to what we are).