“Philosophical decisions,” says David Hume toward the end of his An Enquiry Concerning Human Understanding, “are nothing but the reflections of common life, methodised and corrected.” This simple, homely epigram conceals a great deal. For one thing, An Enquiry Concerning Human Understanding is actually a sort of popularized revision of ideas that were systematically developed in book 1 of his precocious A Treatise of Human Nature (1739-1740), which, although it was completed before the author was twenty-five, has been characterized as one of the most profound, thoroughly reasoned, and purely scientific works in the history of philosophy. Second, Hume’s method for correcting the reflections of common life actually involves a thorough attack on the obscurities of metaphysical idealists.
Born in an age of reason, Hume at first shared the optimism of those who were certain that pure reason could unlock the secrets of nature, and as he read Francis Bacon, John Newton, Thomas Hobbes, and John Locke, he longed for fame equal to theirs. However, as he reported in a letter to Sir Gilbert Elliot, although he “began with an anxious search after arguments, to confirm the common opinion; doubts stole in, dissipated, returned; were again dissipated, returned again; and it was a perpetual struggle of restless imagination against inclination, perhaps against reason.” That last, “perhaps against reason,” is the crucial phrase, for no philosopher before Hume used reason so brilliantly in an attack against the certainties of reason. The twelve essays of An Enquiry Concerning Human Understanding reflect Hume’s three principal attacks against rationalism: against the doctrine of innate ideas and faith in ontological reasoning and an ordered universe; against empiricism, both the kind that led to Lockean dualism and the kind that led to Berkeleyan idealism, on the ground that neither the physical nor the spiritual can be proved; and against deism, based on universal axioms and the law of causality. It is not surprising that religions since Hume have largely made their appeals to faith rather than to reason.
Considering what remains when such thoroughgoing skepticism rejects so much of the beliefs of rational human beings, Hume himself readily admitted (in the fourth essay, “Sceptical Doubts Concerning the Operations of the Understanding”) that as a man he was quite satisfied with ordinary reasoning processes but that as a philosopher he had to be skeptical, for reasoning was not based on immediate sense experience. “The most lively thought is still inferior to the dullest sensation,” he asserted in his second essay, “The Origin of Ideas.” Unless the mind is “disordered by disease or madness,” actual perceptions have the greatest “force and vivacity,” and it is only on such matters of basic mental fact rather than on the abstract relations of ideas, as in mathematics, that human beings must depend for certainties about life. No amount of reasoning, for example, could have led Adam in the Garden of Eden to believe that fluid, transparent water would drown him or that bright, warm fire would burn him to ashes. “No object ever discovers, by the qualities which appear to the senses, either the causes which produced it, or the effects which arise from it.” In dealing with this idea, Hume doggedly backs every argument into a corner, into some “dangerous dilemma.” What is more, he enjoys himself immensely while doing it—“philosophers that gave themselves airs of superior wisdom and sufficiency, have a hard task when they encounter persons of inquisitive dispositions,” he says. Concerning cause and effect, he argues that similar effects are expected from causes that appear similar, yet this relationship does not always exist and, even when observed, is not reasoned. Furthermore, it is merely an arbitrary assumption, an act of faith, that events that are remembered as having occurred sequentially in the past will...
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