Journal of the History of Philosophy

The Rational Warrant for Hume's General Rules MARIE A. MARTIN 1. INTRODUCTION IT HASBEENTWENTY-THREEYEARSsince Thomas Hearn's now classic article on Hume's general rules first appeared in thisjournal.' The article appeared at a time of renewed interest in Hume's philosophy, interest sparked, in large part, by Norman Kemp Smith's monumental book on Hume., Kemp Smith, while conceding the importance of the "negative" or skeptical side of Hume's thought, turned the attention of philosophers to the positive aspects of his philosophy, those aspects that have since come to be known as Hume's naturalism . The significance of Hearn's article is that it was the first to offer a solution to a problem that threatened to reduce this supposed positive, naturalistic element of Hume's philosophy to simply another form of negative, skeptical irrationalism. What exactly was this problem? A brief look at the relation between Hume's theory of the understanding and that of his Cartesian predecessors should make it clear. Hume's theory of the understanding is, in part, a development of the Cartesian or, more specifically, Malebranchian theory of natural judgments.s According to Descartes and Malebranche, it is the mind or soul that thinks and perceives. The ideas involved in thinking and perceiving come from two sources: from the mind itself, and from the senses. The first sort are the ideas of the intellect or pure understanding. It is by these ideas that we obtain "scientific" knowledge or truth about the nature or essence of objects. The Thomas K. Hearn, Jr., " 'General Rules' in Hume's Treatise,"Journal oft.heHistoryofPhilosophy 8 (197o). ' Norman Kemp Smith, ThePhilosophyofDavid Hume (New York: Macmillan, 1964). sFor a fuller discussion of the relation between the rationalist's theory of natural judgments and Hume's theory see John P. Wright, The ScepticalRealismofDavidHume (Minneapolis: University of Minnesota Press, 1983) and Charles J. McCracken, Malebrancheand British Philosophy(Oxford : Clarendon Press, 1976). [2451 946 JOURNAL OF THE HISTORY OF PHILOSOPHY 31"2 APRIL 1993 second sort of ideas are obtained when the mind directs its attention to the body and perceives by the sense or imagination. These ideas are intimately tied to the psychophysiological mechanisms of the body and are the source of what Malebranche calls 'Judgments of sense," 'Judgments of imagination," or, more generally, "natural judgments." Malebranche's concern was to show how ideas come to be arbitrarily joined together by the body's natural mechanisms, thus proving a major source of error. One example of what he took to be such an arbitrary connection of natural judgment was later made famous by Hume. According to Malebranche : "Men never fail to judge that a thing is the cause of a given effect when the two are conjoined .... This is why everyone concludes that a moving ball which strikes another is the true and principle cause of the motion it communicates to the other .... "4 Malebranche, like Descartes, emphatically denied that sense or imagination can ever be the source of genuine knowledge, which for both meant knowledge of essences. Sense and imagination depend entirely on the body and are provided by a benevolent deity solely for the preservation of the body. They are meant to give us only limited truths about the relation of objects to our bodies. Natural judgments are adequate for this purpose--they help preserve the body. But even in this capacity they are likely to lead us into serious error and require constant regulation and correction by the intellect.5 As is well known, Hume rejected the notion of a Cartesian intellect. He also eschewed any appeal to the supposed intent of a benevolent deity to guarantee the veracity, however limited, of natural judgments. Thus, if Hume's theory of the understanding is to escape being a form of irrationalism where all judgments amount to no more than an arbitrary joining of ideas by purely natural mechanisms, he must provide some means of distinguishing those natural judgments that are reasonable or rationally warranted from those that are unreasonable, irrational, or lacking rational warrant. Hearn's article addressed just this point. General rules, Hearn argued, 4Nicholas Malebranche, The Search after Truth, trans. Thomas Lennon and Paul Olscamp...