Objections to Determinism: I

Abstract

the first objection that we shall consider is one that was raised in the middle ages by St. Thomas Aquinas. One of the reasons he advanced for rejecting the theory that all human acts were the outcome of necessity was that, if this were so, rational deliberation would be impossible. A concise modern version of this argument was put by a philosophically minded biologist, the late Professor J. B. S. Haldane:

If my mental processes are determined wholly by the motions of atoms in my brain, I have no reason to suppose that my beliefs are true … and hence I have no reason for supposing my brain to be composed of atoms.¹⁵

This very concisely stated piece of reasoning purports to turn the tables on the determinist by showing that his theory logically entails that it must itself be false. Hence, by a well-known rule of logic, it must indeed be false since no true statement can entail its own falsity. This argument has been put in various forms by a number of writers, and it is well worth a close examination as it raises some of the key questions that underly the problem of free will and make it interesting.