He never really fails to do it, does he? Even when his style is at its most jocose, Chesterton can give you something to think about.
The latest book of his to hit my "books in progress" shelf is his biography of St. Thomas Aquinas. It's only my first read through of course, but I think it may become a favorite of mine, largely because I find it one of his most convincing.
The chapters exploring Thomas' philosophy are worth reading by themselves, being admirably succint. Chesterton manages to distill the main points driving Thomas' philosophy, and to really explain them, with all the clarity of a teacher who genuinely understands the subject matter. Although his arguments do suffer occasionally from generalizations, this results merely from the brevity of his treatment, and none of these generalizations are lacking plenty of arguments in their favour made by other authors.
Anyway, one such philosophy chapter particularly struck me. Chesterton focuses on the distinctive character of Thomas' thought. According to him, this distinction lies in Thomas' emphasis upon the permanency of being. Thomas' starting point could perhaps be summed up in the very common-sense statement "There is and IS". The world and the realities it contains are solid and true. (I say the "realities it contains" because the influence of evil certainly has left an imprint in the form of absence of good, absence of beauty, absence of reality.)
For Thomas, a single object such as a plain rock is true, not because it is a symbol of some abstract reality, or is a rock in spite of its gray-ness or hardness or any other physical characteristic. It has genuine existence as a rock; its essense is that of a rock and its physical characteristics are in integral part of that identity.
Many ancient philosophers focused entire schools of thought around the concept of the constancy of change. According to some the only consistent truth was the fact that everything was constantly changing or "in flux" - really, this was a wicked common idea, it seems if Fr. Copleston's "History of Philosophy" is accurate. The general impression schools like these would give is that the material world is untrustworthy at best, and that to put faith in things like the senses or even common sense, is a rather naive gesture.
Considering that the majority of even more Catholic philosophies subsequent to these have concentrated on the intellectual life, the soul, or the superiority of the mind, it's likely enough that some of this tendency results from the aforementioned ancient Greeks and their contemporaries.
Fortunately for us, we have Thomas, showing in his dry, matter-of-fact, penetrating prose the Catholic view on the constancy of being. We see change all the time in this world, not because change is the supreme reality, but because the intensely real "is-ness" of every created thing is flawed by some absence of its intended perfection. Evil produces imperfections, but God, in bringing creation back to Himself, allows change in order to return everything to its intended state of being.
Moreover, change (in the ideal form of growth rather than regression or some such thing) exists because even in any object's ideal state of being, it is not Being itself. A created object is not at any time all that it could BE. These are very imprecise terms; they give only the barest approximation of what Chesterton is talking about. Chesterton himself puts it: "Things change because they are not complete; but their reality can only be explained as part of something that is complete. It is God."
Being is real, there is and IS. God is the Supreme Being, as trancendentalist and the term may sound. He is I AM. Acceptance of this fact provides a jumping off point for Thomas.
The amazing thing is, although Thomas' view may require leap of faith, what is in the end more common-sense than his premise: "There is an IS"?