Right off the bat in the Summa Theologiae, St. Thomas rejects rationalism.
It was necessary for man’s salvation that there should be a knowledge revealed by God besides philosophical science built up by human reason. Firstly, indeed, because man is directed to God, as to an end that surpasses the grasp of his reason: “The eye hath not seen, O God, besides Thee, what things Thou hast prepared for them that wait for Thee” (Isaiah 64:4). But the end must first be known by men who are to direct their thoughts and actions to the end. Hence it was necessary for the salvation of man that certain truths which exceed human reason should be made known to him by divine revelation. Even as regards those truths about God which human reason could have discovered, it was necessary that man should be taught by a divine revelation; because the truth about God such as reason could discover, would only be known by a few, and that after a long time, and with the admixture of many errors. Whereas man’s whole salvation, which is in God, depends upon the knowledge of this truth. Therefore, in order that the salvation of men might be brought about more fitly and more surely, it was necessary that they should be taught divine truths by divine revelation. It was therefore necessary that besides philosophical science built up by reason, there should be a sacred science learned through revelation. [I, q.1, a.1]
There are truths that are beyond man’s ability to grasp, and if we are to know them at all they must be revealed to us. Consequently the Christian Faith isn’t rationalist either: man does not define the content of the Faith—of those truths that God reveals to us.
We also see here something that we briefly noticed in a previous post on the opening of the Summa Contra Gentiles: it is difficult for us to attain knowledge. This being the case, God doesn’t merely reveal to us things that we could know in no other way than by revelation; He also declares to us things that we could know by way of reason. Consequently there is some overlap between the things discoverable by reason absolutely speaking and those things we could know only by way of revelation.
Rationalism in this context is not secular humanism, but Aristotelian methodology. It is the reliance of more on logic than empirical observation. Obviously any Christian believes in the necessity of revelation. Marxists are a good example of people who rejected logical rationalism, yet are staunch “secular humanists”. They do so, to shut up anyone with scientific findings. “Oh, you just hate black people, that’s all”
As it turns out upon re-reading the post, I was pretty much completely vague about what I meant by the term rationalist. For that I apologize. I am not even sure that was the best word to express what I actually meant, especially since it usually contrasts with empiricism (which is not a subject Aquinas has in mind in the passage quoted). I think you hit upon the right word though. I meant to say that Aquinas was no rationalist in the sense of being a humanist: he did not believe that all truths were accessible to human reason, nor that man is the final judge of what truth actually is. With respect to Aristotle, I think you would find that Aquinas follows him as far as he can without compromising the faith. Reading Aristotle’s Physics alongside Aquinas’s Summa contra Gentiles makes the latter’s dependence upon Aristotle pretty obvious.
Following Aristotle St. Thomas relies upon both as far as revelation allows.
My post was inspired at least in part by those Schaefferites who follow their mentor in mistakenly attributing the rise of modern philosophy to Aquinas rather than to Descartes, by erroneously claiming that Aquinas held to a view of reason as independent of the authority of revelation. This is not the case, as I hope the post shows.