PSR and intelligibility

Question

"Everything is intelligible"

• Jacques Maritain

From a thomistic point of view and given the doctrine of transcendentals, it seems that everything is intelligible (PSR formulation). But from the fact that everything is intelligible, how does it follow that "there is a sufficient reason or adequate necessary objective explanation for the being of whatever is and for all attributes of any being” (Bernard Wuellner, Dictionary of Scholastic Philosophy, p. 15)?

How do these two formulations relate? If I say that being A or event X lacks a reason or explanation why is that unintelligible?

*According to Edward Feser and his "Scholastic Metaphysics", "on the Scholastic doctrine of the transcendentals, being is convertible with truth (Cf. Bittle 1939, Part II; Feser 2009, pp. 31-36; Gardeil 1967, Chapter 4; Koren 1960, Chapter 2; Renard 1946, Section IV)".

"A transcendental notion is one which is above every genus, common to all things and thus not restricted to any category or individual. Being is a transcendental insofar as everything real, whether a substance, an accident, or whatever, is a being of some sort or other. Truth is also a transcendental insofar as everything real is truly the thing it is. (Consider how “true” is often used in the sense of “real” or “genuine.”) Being and truth are convertible in the sense that they are the same thing considered under different aspects. Being is reality considered in itself, truth is reality considered in its relation to an intellect which grasps it. In other words, truth is just being considered as intelligible. Now if every being is in this sense true – and that this is Aquinas’s own view is uncontroversial – then it follows that every being is intelligible. And that is just what PSR says. (Cf. Gardeil 1967, pp. 139-42; Maritain 1939, pp. 97-105)".

Answer 1

Intelligible means able to be understood.To understand a particular being, you have to understand both its existence and essence, for that is what makes it different from other beings.

For eg., a horse is different from boar because of different properties (essence) and is different from an imaginary horse because of its existence.

Now, what is meant by understanding something?

It means to have reasons why is something the way it is, and not the other way (which reflects Correspondence Theory of Truth). That is however, what we mean by explanation, for explanation means justification, and justification is an act of showing (via reasoning) why something is the way it is, and not the other way.

Edit -

For something to be intelligible, it must align with our current knowledge or belief. For example, a writing on a stone tablet is only intelligible, if we know the language or what characters mean.

So, for something to be understood by us it must follow from our already present set of knowledge 'K' or beliefs 'B', via an explanation 'E' or justification 'J', for we can only understand things in terms of what we already know or believe. Like an uneducated person can only understand scientific concepts in there mere abstractions that is available to him. For if there is no explanation 'E' or justification 'J' of that thing, then the thing is identical with our knowledge 'K' or belief 'B'.

So, if something is not part of our knowledge 'K' or belief 'B', then for it to be intelligible/understandable, it must have an explanation 'E' or justification 'J'.