But Berkeley in turn was followed by David Hume, who drove the empiricist epistemological critique to its final extreme, making use of Berkeley’s insight while turning it in a direction more characteristic of the modern mind—more reflective of that secular skepticism growingly visible from Montaigne through Bayle and the Enlightenment. As an empiricist who grounded all human knowledge in sense experience, Hume agreed with Locke’s general orientation, and he agreed too with Berkeley’s criticism of Locke’s theory of representation; but he disagreed with Berkeley’s idealist solution. Human experience was indeed of the phenomenal only, of sense impressions, but there was no way to ascertain what was beyond the sense impressions, spiritual or otherwise. Like Berkeley, Hume could not accept Locke’s views on representative perception, but neither could he accept Berkeley’s identification of external objects with internal ideas, rooted ultimately in the mind of God.
To begin his analysis, Hume made a distinction between sensory impressions and ideas: Sensory impressions are the basis of any knowledge, and they come with a force and liveliness that make them unique. Ideas are faint copies of those impressions. One can experience through the senses an impression of the color blue, and on the basis of this impression one can have an idea of that color whereby the latter can be recalled. The question therefore arises, What causes the sensory impression? If every valid idea has a basis in a corresponding impression, then to what impression can the mind point for its idea of causality? None, Hume answered. If the mind analyzes its experience without preconception, it must recognize that in fact all its supposed knowledge is based on a continuous chaotic volley of discrete sensations, and that on these sensations the mind imposes an order of its own. The mind draws from its experience an explanation that in fact derives from the mind itself, not from the experience. The mind cannot really know what causes the sensations, for it never experiences “cause” as a sensation. It experiences only simple impressions, atomized phenomena, and causality per se is not one of those simple impressions. Rather, through an association of ideas—which is only a habit of the human imagination—the mind assumes a causal relation that in fact has no basis in a sensory impression. All that man has to base his knowledge on is impressions in the mind, and he cannot assume to know what exists beyond those impressions.
Hence the presumed basis for all human knowledge, the causal relation, is never ratified by direct human experience. Instead, the mind experiences certain impressions that suggest they are caused by an objective substance existing continuously and independently of the mind; but the mind never experiences that substance, only the suggestive impressions. Similarly, the mind may perceive that one event, A, is repeatedly followed by another event, B, and on that basis the mind may project that A causes B. But in fact all that is known is that A and B have been regularly perceived in close association. The causal nexus itself has never been perceived, nor can it be said to exist outside of the human mind and its internal habits. Cause must be recognized as merely the accident of a repeated conjunction of events in the mind. It is the reification of a psychological expectation, apparently affirmed by experience but never genuinely substantiated.
Even the ideas of space and time are ultimately not independent realities, as Newton assumed, but are simply the result of experiencing the coexistence or succession of particular objects. From repeated experiences of this kind, the notions of time and space are abstracted by the mind, but actually time and space are only ways of experiencing objects. All general concepts originate in this way, with the mind moving from an experience of particular impressions to an idea of relationship between those impressions, an idea that the mind then separates and reifies. But the general concept, the idea, is only the result of the mind’s habit of association. At bottom, the mind experiences only particulars, and any relation between those particulars is woven by the mind into the fabric of its experience. The intelligibility of the world reflects habits of the mind, not the nature of reality.
Part of Hume’s intention was to refute the metaphysical claims of philosophical rationalism and its deductive logic. In Hume’s view, two kinds of propositions are possible, one based purely on sensation and the other purely on the intellect. A proposition based on sensation concerns obvious matters of concrete fact (e.g., “it is a sunny day”), which are always contingent (they could have been different, though in fact they were not). By contrast, a proposition based purely on intellect concerns relations between concepts (e.g., “all squares have four equal sides”), and these are always necessary—that is, their denial leads to self-contradiction. But the truths of pure reason, such as those of mathematics, are necessary only because they exist in a self-contained system with no mandatory reference to the external world. They are true only by logical definition, by making explicit what is implicit in their own terms, and these can claim no necessary relation to the nature of things. Hence the only truths of which pure reason is capable are tautological. Reason alone cannot assert a truth about the ultimate nature of things.
Moreover, not only does pure reason have no direct insight into metaphysical matters, neither can reason pronounce on the ultimate nature of things by inference from experience. One cannot know the supersensible by analyzing the sensible, because the only principle upon which one can base such a judgment—causality—is finally grounded only in the observation of particular concrete events in temporal succession. Without the elements of temporality and concreteness, causality is rendered meaningless. Hence all metaphysical arguments, which seek to make certain statements about all possible reality beyond temporal concrete experience, are vitiated at their basis. Thus for Hume, metaphysics was just an exalted form of mythology, of no relevance to the real world.
But another and, for the modern mind, more disturbing consequence of Hume’s critical analysis was its apparent undermining of empirical science itself, for the latter’s logical foundation, induction, was now recognized as unjustifiable. The mind’s logical progress from many particulars to a universal certainty could never be absolutely legitimated: no matter how many times one observes a given event-sequence, one can never be certain that that event-sequence is a causal one and will always repeat itself in subsequent observations. Just because event B has always been observed to follow event A in the past cannot guarantee it will always do so in the future. Any acceptance of that “law,” any belief that the sequence represents a true causal relationship, is only an ingrained psychological persuasion, not a logical certainty. The apparent causal necessity in phenomena is the necessity only of subjective conviction, of the human imagination controlled by its regular association of ideas. It has no objective basis. One can perceive the regularity of events, but not their necessity. The latter is no more than a subjective feeling induced by the experience of apparent regularity. In such a context, science is possible, but it is a science of the phenomenal only, of appearances registered in the mind, and its certainty is a subjective one, determined not by nature but by human psychology.
Paradoxically, Hume had begun with the intention of applying rigorous Newtonian “experimental” principles of investigation to man, to bring the successful empirical methods of natural science to a science of man. But he ended by casting into question the objective certainty of empirical science altogether. If all human knowledge is based on empiricism, yet induction cannot be logically justified, then man can have no certain knowledge.
With Hume, the long-developing empiricist stress on sense perceptions, from Aristotle and Aquinas to Ockham, Bacon, and Locke, was brought to its ultimate extreme, in which only the volley and chaos of those perceptions exist, and any order imposed on those perceptions was arbitrary, human, and without objective foundation. In terms of Plato’s fundamental distinction between “knowledge” (of reality) and “opinion” (about appearances), for Hume all human knowledge had to be regarded as opinion. Where Plato had held sensory impressions to be faint copies of Ideas, Hume held ideas to be faint copies of sensory impressions. In the
long evolution of the Western mind from the ancient idealist to the modern empiricist, the basis of reality had been entirely reversed: Sensory experience, not ideal apprehension, was the standard of truth- and that truth was utterly problematic. Perceptions alone were real for the mind, and one could never know what stood beyond them.
Locke had retained a certain faith in the capacity of the human mind to grasp, however imperfectly, the general outlines of an external world by means of its combining operations. But for Hume, not only was the human mind less than perfect, it could never claim access to the world’s order, which could not be said to exist apart from the mind. That order was not inherent in nature, but was the result of the mind’s own associating tendencies. If nothing was in the mind that did not ultimately derive from the senses, and if all valid complex ideas were based on simple ideas derived from sensory impressions, then the idea of cause itself, and thus certain knowledge of the world, had to be critically reconsidered, for cause was never so perceived. It could never be derived from a simple direct impression. Even the experience of a continuously existing substance was only a belief produced by many impressions’ recurring in a regular way, producing the fiction of an enduring entity.
Pursuing this psychological analysis of human experience still further, Hume concluded that the mind itself was only a bundle of disconnected perceptions, with no valid claims to substantial unity, continuous existence, or internal coherence, let alone to objective knowledge. All order and coherence, including that giving rise to the idea of the human self, were understood to be mind-constructed fictions. Human beings required such fictions to live, but the philosopher could not substantiate them. With Berkeley, there had been no necessary material basis for experience, though the mind had retained a certain independent spiritual power derived from God’s mind, and the world experienced by the mind derived its order from the same source. But with the more secular skepticism of Hume, nothing could be said to be objectively necessary—not God, not order, not causality, nor substantial existents, nor personal identity, nor real knowledge. All was contingent. Man knows only phenomena, chaotic impressions; the order he perceives therein is imagined, for reasons of psychological habit and instinctual need, and then projected. Thus did Hume articulate philosophy’s paradigmatic skeptical argument, one that in turn was to stimulate Immanuel Kant to develop the central philosophical position of the modern era.
Kant
The intellectual challenge that faced Immanuel Kant in the second half of the eighteenth century was a seemingly impossible one: on the one hand, to reconcile the claims of science to certain and genuine knowledge of the world with the claim of philosophy that experience could never give rise to such knowledge; on the other hand, to reconcile the claim of religion that man was morally free with the claim of science that nature was entirely determined by necessary laws. With these several claims in such intricate and pointed conflict, an intellectual crisis of profound complexity had emerged. Kant’s proposed resolution of that crisis was equally complex, brilliant, and weighty in its consequences.
Kant was too intimate with Newtonian science and its triumphs to doubt that man had access to certain knowledge. Yet he felt as well the force of Hume’s relentless analysis of the human mind. He too had come to distrust the absolute pronouncements on the nature of the world for which a purely rational speculative metaphysics had been pretending competence, and concerning which it had fallen into endless and seemingly irresolvable conflict. According to Kant, the reading of Hume’s work had awakened him from his “dogmatic slumber,” the residue of his long training in the dominant German rationalist school of Wolff, Leibniz’s academic systematizer. He now recognized that man could know only the phenomenal, and that any metaphysical conclusions concerning the nature of the universe that went beyond his experience were unfounded. Such propositions of the pure reason, Kant demonstrated, could as readily be opposed as supported by logical argument. Whenever the mind attempted to ascertain the existence of things beyond sensory experience—such as God, the immortality of the soul, or the infinity of the universe—it inevitably found itself entangled in contradiction or illusion. The history of metaphysics was thus a record of contention and confusion, entirely devoid of cumulative progress. The mind required empirical evidence before it could be capable of knowledge, but God, immortality, and other such metaphysical matters could never become phenomena; they were not empirical. Metaphysics, therefore, was beyond the powers of human reason.
But Hume’s dissolution of causality also appeared to undercut the claims of natural science to necessary general truths about the world, since Newtonian science was based on the assumed reality of the now uncertified causal principle. If all human knowledge necessarily came from observation of particular instances, these could never be legitimately generalized into certain laws, since only discrete events were perceived, never their causal connection. Nevertheless, Kant was convinced beyond doubt that Newton, with the aid of experiments, had gotten hold of real knowledge of absolute certainty and generality. Who was correct, Hume or Newton? If Newton had attained certain knowledge, and yet Hume had demonstrated the impossibility of such knowledge, how could Newton have succeeded? How was certain knowledge possible in a phenomenal universe? This was the burden of Kant’s Critique of Pure Reason, and his solution was to satisfy the claims of both Hume and Newton, of skepticism and science—and in so doing to resolve modern epistemology’s fundamental dichotomy between empiricism and rationalism.
The clarity and strict necessity of mathematical truths had long provided the rationalists—above all Descartes, Spinoza, and Leibniz—with the assurance that, in the world of modern doubt, the human mind had at least one solid basis for attaining certain knowledge. Kant himself had long been convinced that natural science was scientific to the precise extent that it approximated to the ideal of mathematics. Indeed, on the basis of such a conviction, Kant himself had made an important contribution to Newtonian cosmology, demonstrating that through strictly necessary measurable physical forces, the Sun and planets had consolidated and assumed the motions defined by Copernicus and Kepler. To be sure, in attempting to extend the mathematical mode of reasoning to metaphysics, Kant became convinced of pure reason’s incompetence in such matters. But within the bounds of sensory experience, as in natural science, mathematical truth was patently successful.
Yet because natural science was concerned with the external world given through the senses, it thereby opened itself to Hume’s criticism that all its knowledge would then be contingent, its apparent necessity only psychological. By Hume’s reasoning, with which Kant had to agree, the certain laws of Euclidean geometry could not have been derived from empirical observation. Yet Newtonian science was explicitly based upon Euclidean geometry. If the laws of mathematics and logic were said to come from within the human mind, how could they be said to pertain with certainty to the world? Rationalists like Descartes had more or less simply assumed a mind-world correspondence, but Hume had subjected that assumption to a damaging critique. Nevertheless, a mind-world correspondence was clearly presupposed, and seemingly vindicated, in the Newtonian achievement, of which Kant was certain.
Kant’s extraordinary solution was to propose that the mind-world correspondence was indeed vindicated in natural science, yet not in the naive sense previously assumed, but in the critical sense that the “world” science explicated was a world already ordered by the mind’s own cognitive apparatus. For in Kant’s view, the nature of the human mind is such that it does not passively receive sense data. Rather, it actively digests and structures them, and man therefore knows objective reality precisely to the extent that that reality conforms to the fundamental structures of the mind. The world addressed by science corresponds to principles in the mind because the only world available to the mind is already organized in accordance with the mind’s own processes. All human cognition of the world is channeled through the human mind’s categories. The necessity and certainty of scientific k
nowledge derive from the mind, and are embedded in the mind’s perception and understanding of the world. They do not derive from nature independent of the mind, which in fact can never be known in itself. What man knows is a world permeated by his knowledge, and causality and the necessary laws of science are built into the framework of his cognition. Observations alone do not give man certain laws; rather, those laws reflect the laws of man’s mental organization. In the act of human cognition, the mind does not conform to things; rather, things conform to the mind.
How did Kant arrive at this epoch-making conclusion? He began by noting that if all content that could be derived from experience was withdrawn from mathematical judgments, the ideas of space and time still remained. From this he inferred that any event experienced by the senses is located automatically in a framework of spatial and temporal relations. Space and time are “a priori forms of human sensibility”: they condition whatever is apprehended through the senses. Mathematics could accurately describe the empirical world because mathematical principles necessarily involve a context of space and time, and space and time lay at the basis of all sensory experience: they condition and structure any empirical observation. Space and time are thus not drawn from experience but are presupposed in experience. They are never observed as such, but they constitute that context within which all events are observed. They cannot be known to exist in nature independently of the mind, but the world cannot be known by the mind without them.
Space and time therefore cannot be said to be characteristic of the world in itself, for they are contributed in the act of human observation. They are grounded epistemologically in the nature of the mind, not ontologically in the nature of things. Because mathematical propositions are based on direct intuitions of spatial relations, they are “a priori”—constructed by the mind and not derived from experience—and yet they are also valid for experience, which will by necessity conform to the a priori form of space. It is true that pure reason inevitably becomes entangled in contradiction if it attempts to apply these ideas to the world as a whole—to ascertain what is true beyond all possible experience—as in trying to decide whether the universe is infinite or finite either in time or space. But as regards the phenomenal world that man does experience, time and spage are not just applicable concepts, they are intrinsic components of all human experience of that world, frames of reference mandatory for human cognition.
Passion of the Western Mind Page 44