infinite regress argument a distinctively philosophical kind of argument purporting to show that a thesis is defective because it generates an infinite series when either (form A) no such series exists or (form B) were it to exist, the thesis would lack the role (e.g., of justification) that it is supposed to play. The mere generation of an infinite series is not objectionable. It is misleading therefore to use ‘infinite regress’ (or ‘regress’) and ‘infinite series’ equivalently. For instance, both of the following claims generate an infinite series: (1) every natural number has a successor that itself is a natural number, and (2) every event has a causal predecessor that itself is an event. Yet (1) is true (arguably, necessarily true), and (2) may be true for all that logic can say about the matter. Likewise, there is nothing contrary to logic about any of the infinite series generated by the suppositions that (3) every free act is the consequence of a free act of choice; (4) every intelligent operation is the result of an intelligent mental operation; (5) whenever individuals x and y share a property F there exists a third individual z which paradigmatically has F and to which x and y are somehow related (as copies, by participation, or whatnot); or (6) every generalization from experience is inductively inferable from experience by appeal to some other generalization from experience. What Locke (in the Essay concerning Human Understanding) objects to about the theory of free will embodied in (3) and Ryle (in The Concept of Mind) objects to about the ‘intellectualist legend’ embodied in (4) can therefore be only that it is just plain false as a matter of fact that we perform an infinite number of acts of choice or operations of the requisite kinds. In effect their infinite regress arguments are of form A: they argue that the theories concerned must be rejected because they falsely imply that such infinite series exist. Arguably the infinite regress arguments employed by Plato (in the Parmenides) regarding his own theory of Forms and by Popper (in the Logic of Scientific Discovery) regarding the principle of induction proposed by Mill, are best construed as having form B, their objections being less to (5) or (6) than to their epistemic versions: (5*) that we can understand how x and y can share a property F only if we understand that there exists a third individual (the ‘Form’ z) which paradigmatically has F and to which x and y are related; and (6*) that since the principle of induction must itself be a generalization from experience, we are justified in accepting it only if it can be inferred from experience by appeal to a higherorder, and justified, inductive principle. They are arguing that because the series generated by (5) and (6) are infinite, the epistemic enlightenment promised by (5*) and (6*) will forever elude us. When successful, infinite regress arguments can show us that certain sorts of explanation, understanding, or justification are will-o’-thewisps. As Passmore has observed (in Philosophical Reasoning) there is an important sense of ‘explain’ in which it is impossible to explain predication. We cannot explain x’s and y’s possession of the common property F by saying that they are called by the same name (nominalism) or fall under the same concept (conceptualism) any more than we can by saying that they are related to the same form (Platonic realism), since each of these is itself a property that x and y are supposed to have in common. Likewise, it makes no sense to try to explain why anything at all exists by invoking the existence of something else (such as the theist’s God). The general truths that things exist, and that things may have properties in common, are ‘brute facts’ about the way the world is. Some infinite regress objections fail because they are directed at ‘straw men.’ Bradley’s regress argument against the pluralist’s ‘arrangement of given facts into relations and qualities,’ from which he concludes that monism is true, is a case in point. He correctly argues that if one posits the existence of two or more things, then there must be relations of some sort between them, and then (given his covert assumption that these relations are things) concludes that there must be further relations between these relations ad infinitum. Bradley’s regress misfires because a pluralist would reject his assumption. Again, some regress arguments fail because they presume that any infinite series is vicious. Aquinas’s regress objection to an infinite series of movers, from which he concludes that there must be a prime mover, involves this sort of confusion. See also EPISTEMIC REGRESS ARGUMENT , INFINITY , VICIOUS REGRES. R.D.B.