Perhaps, too, as difficulties are of two kinds, the cause of the presentAristotle and Thomas are commenting on how reaching the truth is both difficult and easy. It is easy (according to Aristotle) in the sense that the sun is the most obvious and visible object in the world. It is so obvious, in fact, that the eyes of a bat are blinded by it, and cannot see it (Thomas mentions owls, and other translations have moles, I think). Thus, the truth is right before us, and in an obvious way. Yet we are blinded by it, and cannot grasp it.
difficulty is not in the facts but in us. For as the eyes of bats are to the
blaze of day, so is the reason in our soul to the things which are by nature
most evident of all.
Is that right? How is this idea related to the distinction between a posteriori and a priori that I discussed here? A priori reasoning is from what is logically prior to what is derivable from it. The exemplar is geometric and mathematical reasoning, and in that sense the truth must be easy, for we begin with self-evident truths, and move from them to other truths which are less evident, but logically deducible. A posteriori reasoning is from effect - typically observed effect - to cause. The exemplar being the truth attained by the natural sciences, which is clearly difficult to get hold of, as I suggested earlier.
But is that what Aristotle has in mind? Probably not. The difficulty of a posteriori investigation - from effect to cause - is precisely because the cause is not visible to us. This is clearly not like the case of the sun. Thomas interprets him as follows:
Obviously, then, the difficulty experienced in knowing the truth is due
principally to some weakness on the part of our intellect. From this it follows
that our soul’s intellectual power is related to those immaterial beings, which
are by nature the most knowable of all, as the eyes of owls are to the light of
day, which they cannot see because their power of vision is weak, although they
do see dimly lighted things.
The analogy is between the weakness of an owl's eye (or a bat's eye, or a mole's eye) and the weakness of our intellect. The difficulty is not a matter to be resolved by scientific investigation, i.e. natural scientific investigation. The problem (according to Thomas) is that the human mind cannot be elevated to the level of knowing the essences (quidditates) of immaterial substances because they are not on the same level as sensible substances. The difficulty is not in things but in us.
And here you have the fundamental problem of understanding the Metaphysics, indeed the problem of understanding the project of all Western philosophy. Is it a fundamentally rational project? But as Hugh Lawson-Tancred says in his excellent introduction to and commentary on the book, "it seems excessively implausible that mere rumination on some of the more elementary features of our quotidian experience could lead to a profound revision of our conception of the universe". Or is it essentially mystical, as the popular meaning of the word metaphysics suggests? More later.