Mortimer J. Adler (St. Thomas and the Gentiles, p. 89):
St. Thomas has no more a system of philosophy than Shakespeare has a point of view or a message. In Shakespeare’s poetry nature is imitated so well, so properly, that all the wide world is presented to us with artistic objectivity. So, too, in the philosophy of St. Thomas the world is laid before us; his thought about it is diaphanous, a perfect medium of vision. In both cases, the art conceals itself by performing its task so well. And in both cases, the art introduces order and proportion into a vast multiplicity of things. Let us not confuse the notion of “system” with the more general idea of a good arrangement of parts. System in the mathematical sense is rigid, selective, exclusive: it has the kind of artificiality which is appropriate only to mathematical objects; but where mathematics deals with the ideal and the possible, philosophy deals with the real and the actual. The real can be ordered by art without distortion; it cannot be systematized.
Etymologies 