Maritain - Knowledge and Being

From Existence and the Existent:

[K]nowledge is immersed in existence. Existence - the existence of material realities - is given us at first by sense; sense attains the object as existing; that is to say, in the real and existing influence by which it acts upon our sensorial organs. This is why the pattern of all true knowledge is the intuition of the thing that I see, and that sheds its light upon me. ... Sense delivers existence to the intellect; it gives the intellect an intelligible treasure which sense does not know to be intelligible, and which the intellect, for its part, knows and calls by its name, which is being (p. 21, emphasis in original).

Our knowledge begins with sensory input, and it is true to the extent that it conforms to that which is perceived by the senses - to reality ("the pattern of all true knowledge is the intuition of the thing that I see"). Contrast this - that truth resides in the conformity of our thoughts to reality - with the presuppositionalist idea that truth consists in the interpretive grid that we impose upon the world around us. One ready example (and I don't mean to pick on the author of it, but this is the first instance of the sort of thing that I mean here that I could think of, and it was easier to find than googling something else up) may be found here, where the author writes:

Ah well, the problem with evidence is that one needs a framework in which to view it.

Well no. One obvious implication in the present context is that truth is subjective: it's a question of your perspective or framework. So how does one know that his framework is correct? That author will say that it his is true because it is (or is based upon) divine revelation. That's fine, but how does he know that he has received divine revelation? One option is that he perceives it by means of his senses, in which case his interpretive framework is initially non-existent (since it would have to be drawn from that external revelation, and he would not possess it until he had drawn it out). But if it is initially non-existent, then (according to the notion he presents above) he would need some other framework in which to view it. How does he know that other framework is reliable for drawing a new, divinely revealed framework out of the revelation? And if that other framework is reliable for that, why is it not generally reliable?

The other option I can imagine would be that this framework is directly revealed to him by God. But how does he know that God (rather than a demon, for example) has revealed it? This is intrinsically subjective - which is precisely my point.

So in the end this seems to be an inherently irrational position. Far better, it seems, is to trust the necessary reliability of our senses, which are our only source of information about the world around us. Far better to say that truth consists in conformity to reality.