One of Aristotle’s chief strengths is also one of his weaknesses. His reliance on the World as We Know It as one of his chief premises is a very good thing, because it saves his philosophical world from being too small and absurdly limited. On the other hand, our understanding of the physical world—the understanding we call “science”, though Aristotle would have meant something much broader by that term—has improved significantly over the past two millenia. And that means that some of his works now seem laughably wrong. No one now reads Aristotle for a deep understanding of astronomy, for example. For Aristotle, the “heavenly bodies” traveled in perfect circular orbits, were incorruptible, and were in fact of a different order of being than the Earth on which we live. No amount of respect for Aristotle as a thinker and philosophy can get past the fact that he was woefully wrong on these points. Nevertheless, it was the best “science” available in his day.

The problem extends to his purely philosophical works (in which category I include his Physics), and by extension to the works of Aquinas, because both of them use examples from astronomy, medicine, and other sciences to illustrate their arguments. Many of these examples consequently sound absurd to us today, which gives the impression that the arguments in which they appear are likewise absurd.

It’s often the case, though, that the example is simply an illustration of a general principle. The example might be obsolete, but that doesn’t invalidate the principle, at least not necessarily. In other cases, the problem is one of terminology rather than of sense. Aquinas, for example, knew nothing of genetics or heredity as we now understand it; but he knew perfectly well that some characteristics are passed by fathers to their children. Some of these examples make perfect sense, if you can get past the language.

There are two important things to remember. The first is that philosophical arguments are logical demonstrations based on sound arguments from general principles. The examples are not intended to be evidence driving a probable conclusion; rather they are intended to illustrate the workings of the general principles and hence to cast light on them and on the argument as a whole. What we here is metaphysical deduction, not scientific induction, but many, especially the scientistically minded, tend to read it as the latter and thus discount it.

The second is that Aristotle really was trying to incorporate the best scientific knowledge of the day. If he could have been brought forward to the 17th century and the “Age of Reason”, he (unlike some of his supporters of that era) would have been thrilled to update his scientific knowledge. His metaphysical principles, however, need not have changed.