Hume's "Dialectic"

139 HUME'S "DIALECTIC" Hume's treatment of contradiction in his discussion of external existence has generally been understood to resemble the Pyrrhonian model of dialectic; consequently, Hume has been viewed as a sceptic and an irrationalist . According to that model of dialectic, the sceptic, by showing that equally strong arguments can be constructed both for and against a proposition, raises doubts about the ability of reason to determine the truth or falsity of 2 beliefs. However, I will argue that Hume's treatment of contradiction differs significantly from Pyrrhonian dialectic. I will further argue that his treatment of contradiction is strongly analogous to the Kantian model of dialectic. According to Kant, dialectic is a method which not only shows that reason generates contradictions but which also provides a critique of 3 the logic generating those contradictions. The goal of Kant's dialectic is thus distinctly different from the goal of Pyrrhonian dialectic. For Kant, dialectic is a method for resolving scepticism. The parallels between Hume's treatment of contradiction and Kant's dialectic will suffice to show that Hume's "dialectic" is also a method for resolving, rather than generating, scepticism. Two features of Pyrrhonian dialectic have been deemed relevant for Hume's treatment of contradiction in his discussion of external existence. The Pyrrhonist argues that (1) if equally strong arguments can be given for and against a proposition, it is impossible to assess the truth or falsity of the proposition on the basis of any argument; and (2) if it 140 is impossible to assess rationally the truth or falsity of propositions, we must content ourselves in practical life with following custom and convention in all matters of opinion. Hume describes the contradiction in our belief in external existence as an opposition between two equally natural and unavoidable modes of inference. Both modes of inference are operations of the imagination. Hume does not give a special name to the first of these modes of inference, but he describes it as an "irregular" inference based upon the resemblance A of two distinct mental operations (T 203-204). The second is reflective, or causal, inference based on observation of the constant conjunction of like objects. Causal reasoning is reflective insofar as it is regulated by rules and is, consequently, a check or monitor for judgments resulting from the irregular or unchecked operation of the imagination. These two principles of inference lead to two different judgments about the nature of our perceptions: The imagination tells us, that our resembling perceptions have a continu'd and uninterrupted existence, and are not annihilated by their absence. Reflection tells us, that even our resembling perceptions are interrupted in their existence, and different from each other. (T 215) Just as the Pyrrhonian sceptic maintains that the constructibility of equally strong arguments establishing contradictory propositions makes it impossible to decide which proposition is true, Hume similarly maintains that two opposing modes of inference have an equal influence on the mind and therefore are "unable mutually to destroy each other" (T 215). However, Hume's account of this contradiction would be Pyrrhonian only if he argued that these principles, in addition to being equal in psychological 141 force, also have the same epistemic status. Only their having the same epistemic status makes it impossible to decide rationally whether one of the two principles is a reliable guide for making sound empirical inferences. Popkin, a defender of the Pyrrhonian reading of Hume, maintains that this is just what Hume does argue. Reflection for Hume, he maintains, is no more -a rational principle than is unchecked imagination: There is no rational basis for believing that those objects that have constantly been conjoined in the past, will be so conjoined in the future. It is only custom, or "a certain instinct of our nature," that makes us believe that they will be so conjoined, and this instinct which may be hard to resist psychologically, may well be fallacious and deceitful. The basis for all factual and probable reasoning is thus irrational. 5 If reflection is as irrational a principle as unchecked imagination, then the opposition between reflection and unchecked imagination would be an opposition between equally irrational principles. Consequently, a...