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CHAPTER 4

A New Scene of Thought

To achieve his purpose, Hume had to show that man had no extraordinary powers like those claimed for him by others. Philosophers as well as the vulgar, Hume declared, felt obliged to assign “some invisible intelligent principle” for anything that surprised them. As they could not understand the effect either of the mind on the body, or of the body on the mind, they asserted that “the Deity is the immediate cause of the union between soul and body.” Sometimes philosophers felt impelled to go further, Hume continued boldly, and they extended “the same inference to the mind itself, in its internal operation.” They described ideas as “nothing but a revelation made to us by our maker.” Rather than trace an idea to the influence of human will, they spoke only of the “universal creator, who discovers it to the mind, and renders it present to us. Thus, according to these philosophers, everything is full of God.”¹ Hume meant to cut the ties between man and God, and restore man to a purely human nature, such as the pagans found sufficient before Christianity removed man into a higher, more spiritual sphere.

It would seem that Hume’s way had been well prepared by Hobbes and Locke, because they are commonly described as empiricists and iconoclasts who broke decisively with the Christian picture of man. Unlike continental philosophers, they were concerned not so much to satisfy purely intellectual curiosity, to discover the true constitution of knowledge or the essence of things, as to condemn certain prevailing intellectual fallacies and their unfortunate moral consequences. They wished in different ways to restrain human speculation within its proper confines, and to correct what Locke called the disposition of men to “let loose their thoughts into the vast ocean of Being.” But from Hume’s standpoint, neither of them provided anything more than a variation on the traditional view.

Hobbes spoke of reasoning, rather than of reason, and he described man as fundamentally a creature of passion, whose well-being was promoted by passion as much as by reasoning; and he was, in a sense, as persuaded of human fallibility as Montaigne. In this respect he belongs, as Hume does, to the sceptical late scholastic tradition.¹ But not only was his emphasis on man’s brutishness uncongenial to Hume; Hobbes offered nothing useful to Hume because his attention was centred on the achievements of reasoning, rather than on exploring the implications of his view that reasoning was concerned solely with causes and effects. Although he defined philosophy modestly as “the establishment by reasoning of true fictions,” he retained unbounded confidence in the truths he allowed it to establish. Hume’s concern was entirely with the nature and limits of reason, and it led him to reverse Hobbes’s conclusions. It made him antagonistic to Hobbes’s geometrical style of argument and to his whole dogmatic manner of dealing with human questions.

Locke’s philosophy was more nearly to Hume’s purpose. He was in the first place temperamentally more congenial, not so possessed as Hobbes was by the pursuit of system, and more inclined to emphasize the folly of human ambitions. Although his philosophy was used by Clarke and others to bolster systems that Hume equated with scholasticism, it was directed against the arrogant verbalism of the schools, the Deism of Lord Herbert founded on innate principles, the sermons and political orations that elevated current prejudices into immutable truths. By attacking the belief in innate ideas and principles, and tracing human knowledge to its origins in sense, Locke’s Essay on Human Understanding stripped away the protection enjoyed by a number of empty abstractions and inherited prejudices, and made it respectable to question elaborate systems. Thus it sanctioned the doubts of those beginning to grow restless under the rule of dogmatic theology, whether of the middle ages or of the Puritans. The disposition that Hume and Locke shared was perfectly expressed in Locke’s statement:

proud man, not content with that knowledge he was capable of, and which was useful to him, would needs penetrate into the hidden cause of things, lay down principles and establish maxims to himself about the operations of nature, and then vainly expect that nature—or in truth God—should proceed according to those laws which his maxims had prescribed to him; whereas his narrow weak faculties could reach no further than the observation and memory of some few facts produced by visible external causes, but in a way utterly beyond the reach of his apprehension;—it being perhaps no absurdity to think that this great and curious fabric of the world, the workmanship of the Almighty, cannot be perfectly comprehended by any understanding but His that made it. Man, still affecting something of the Deity, laboured by his imagination to supply what his observation and experience failed him in; and when he could not discover the principles, causes, and methods of Nature’s workmanship, he would needs fashion all those out of his own thought, and make a world to himself, framed and governed by his own intelligence. … They that are studiously busy in the cultivating and adorning such dry barren notions are vigorously employed to little purpose.¹

Many of the practical conclusions that Locke drew from his philosophy were pleasing to Hume. Since human knowledge falls short of perfectly comprehending what exists, men ought not to think they were at the centre of the universe or try to capture a timeless insight into the whole. They had better reconcile themselves to their more modest powers which vouchsafed them only very partial glimpses of truth. They should concentrate on what they could learn by experience and observation, in order to improve the useful arts, and not yearn to know more. For knowledge of the quality of things was beyond their reach, and served only to employ “idle or over-curious brains. All our business lies at home.”²

But the other, positive purpose of Locke’s philosophy was just what Hume set out to combat. For Locke intended also that his survey of human understanding and powers “to see to what things they are adapted” would show that although men had not the full blaze of sun to light their way, yet “the candle that is set up in us shines bright enough for all our purposes.”³ He was concerned to defeat not only the pretensions of the scholastics, but also the apparent amorality of Hobbes. And against Hobbes, he argued that man was after all a rational creature, who could discern through his reason a certain and universal moral law. Human powers were not great enough to put any conclusion beyond rational criticism, but man could perfectly well rely on his own powers to guide him in ordinary life and particularly in moral questions. Thus Locke hoped, while clearing away false notions, “to raise an edifice uniform and consistent.”

His new edifice, however much it seemed to depart from the established picture of man, still emphasized man’s affinity to God. Locke made sensation the first and most primitive source of ideas, but not the sole source of knowledge. It was supplemented not only by another passive power, reflection—“the capacity of the mind to receive impressions made on it by its own operations,” but also by an active power of the mind, intellect, which created ideas of relation—abstract, general, and universal ideas. Repeatedly, Locke reminded his readers that neither sensation nor reflection could produce general or abstract ideas, and that the power of producing them distinguished man from brutes: “this, I think, I may be positive in, that the power of abstracting is not at all in them [brutes]; and that the having of general ideas is that which puts a perfect distinction betwixt man and brutes, and is an excellence which the faculties of brutes do by no means attain to.…”¹ The idea of cause, that is, of the power to cause change, he pointed out, could not be resolved into either sensation or reflection; the mind added to the materials supplied by sensation and reflection an idea of its own creation, the idea of cause and effect. The idea of substance was also admitted by Locke, and made equally independent of sensation and reflection. “I never said that the general idea of substance comes in by sensation and reflection or that it is a simple idea of sensation or reflection,” he replied sharply to the criticism of the Bishop of Worcester, “for general ideas come not into the mind by sensation or reflection, but are the creatures or inventions of the understanding, as I think I have shown.”² For all his talk of the dependence of ideas on sensation, intuition was, after all, fundamental for Locke. It furnished all the basic principles of certainty and knowledge.³

Locke’s moral theory, which Clarke took over, depended entirely on the assumption that man has a rational faculty linking him to God. Reason was declared to be “natural revelation where the eternal Father of light and fountain of all knowledge communicates to mankind that portion of truth which he had laid within the reach of their natural faculties.”⁴ For Locke, no less than for the Cambridge Platonists, reason was “the Candle of the Lord” in man; it alone could discover the law by which he was to govern himself. As this law was nothing other than the rule God had set down for the governance of man, the nature of God and of virtue were one. Thus morality without God was unthinkable. That was why, despite his desire to extend toleration, Locke excluded atheists: “The taking away of God, though but even in thought, dissolves all. …”¹ And for the same reasons, Locke counselled parents to teach their children how to make their irrational, sensual, animal natures submit to the rule of reason.

Locke nevertheless performed a most useful service for Hume. By distinguishing the creative, intuitive, synthetic powers of the mind from the passive, discursive, analytic powers of reflection and demonstration, Locke defined Hume’s problem. “Creative” reason was what the ancients called “logos” or “nous,” that is, the faculty of apprehending necessary truths, of discovering the essence of things, the permanent causes or reasons for the existence of facts experienced by the senses. It enabled man to transcend both matter and mortality, and to deal with eternal things—first causes, human destiny, the relation between man and God. Reason was man’s participation in the supreme rational power that shaped the universe, that imposed order on the chaos of matter and directed the world towards a rational end. Whereas the senses, memory, and imagination, which man shared with animals, enabled him to perceive individual things and to remember and collect his impressions, his intellect apprehended the principle of these things. It gave him knowledge of general truth that was not merely the sum of particular truths but a genuine insight into the nature of things, into final and formal causes.

In order to sever man from God, Hume saw that he needed only to deny “creative” reason. He could then redefine reason as a more limited power to receive ideas, to compare and analyse them, a power that was impressive and distinctive but did not carry man beyond nature. The result would be a “com pleat system of the sciences, built on a foundation almost entirely new, and the only one upon which they can stand with any security.”²

Since in the terms of Locke’s analysis, the work of the creative intellect was to frame abstract ideas and discover relations, these operations absorbed Hume’s attention. If he could have traced them to some faculty other than intuitive reason, he would have destroyed the argument for placing man above the rest of nature and near to God.

At the height of his philosophic enthusiasm, Hume was moved by an ambition to follow the method of Newton, “the greatest and rarest genius that ever rose for the ornament of the species,” who had admitted “no principles but such as were founded on experiment.”¹ He too would disdain any traffic with occult qualities and reduce all phenomena to the simplest causes without, however, probing too far. In this mood, he produced a largely mechanistic analysis of mental phenomena. He began by calling Locke’s ideas “perceptions,” and resolved them into two kinds, “impressions” and “ideas.” Impressions included all the “sensations, passions, and emotions as they make their first appearance in the soul”; ideas were the images of these perceptions in thinking and reasoning. Ideas and perceptions were analogous to physical atoms, simple and separable, but connected by association, “a kind of attraction which in the mental world will be found to have as many extraordinary effects as in the natural, and to shew itself in as many and as various forms.”² The rest of the Treatise was devoted to showing that every activity of the mind could be explained without recourse to reason in the traditional sense. To this end, Hume occupied himself primarily with two topics, “Space and Time” and “Causation.”

The ideas of space and time had always been taken for a prime example of abstract ideas, for they included the notion of infinity and seemed more than any other idea to go beyond the natural capacities of the mind. The human mind was finite, and yet it seemed able to conceive of infinity; in many of its operations it depended on sensation, and yet it had an idea of a vacuum or space where there was nothing that could give rise to sensation. Thus the ideas of space and time had the “air of a paradox,” were “contrary to the first and most unprejudic’d notions of mankind,” and therefore, Hume explained, “greedily embrac’d by philosophers,” as showing the superiority of their science, “which coul’d discover their opinions so remote from vulgar conceptions.”³

Causation was crucial for Hume because it was the only idea of relation that seemed to involve a truly intellectual element. All the others Hume showed to be merely a comparison of ideas or impressions received through sensation. With these mental operations, he had no quarrel, as they implied no creative power of the mind to add something of its own, but merely a power to receive and manipulate ideas. Hume took pains to point out that mathematics was a case of the latter, that there was nothing remarkable in the ability to think of a triangle. Mathematicians liked to pretend that the objects they dealt with were “of so refin’d and spiritual a nature,” that they “must be comprehended by a pure and intellectual view, of which the superior faculties of the soul are alone capable.”¹ Philosophers welcomed this notion, and used it to explain our abstract ideas. But to refute them, Hume declared, one need only remember “that all our ideas are copy’d from our impressions.”² The mathematical idea of a triangle was derived from experience of real triangles, and made abstract in the usual way, which Hume hoped to illustrate by his treatment of space and time. He dismissed also relations of identity and of time and place, because they were comparisons that could be made merely by looking at the two objects. As they involved nothing more than “a mere passive admission of the impressions thro’ the organs of sensation,” the mind had no need to go beyond what was immediately present to the senses.³

It was different, however, with causation. There something more seemed really to be involved and all our knowledge depended on it. For in making a causal inference, we go beyond direct experience to assert that what was true yesterday and today would also be true tomorrow. All our conclusions about matters of fact beyond observations of what is immediately present depend on assumptions about cause and effect. We assume that because such an object had always been attended with such an effect, other similar objects would be attended with similar effects, and thus regularly go beyond memory and sense: “Should it be said that, from a number of uniform experiments, we infer a connexion between the sensible qualities and the secret powers; this, I must confess, seems the same difficulty couched in different terms. The question still recurs. … Where is the medium, the interposing ideas which join propositions so very wide of each other?”¹ Or, in terms of traditional logic, what is the source of the middle term, the definition that makes our syllogisms about cause and effect possible? Rationalist philosophers explained that the intellect grasped intuitively the relation between cause and effect. Reason, by understanding the nature of the cause, they said, could see the necessity of the effect, or, it could see from the character of the event what had to be the nature of the cause. To make the causal inference, and arrive at knowledge beyond empirical verification, to discover the definitions of things was the acknowledged function of reason.

Hume was not alone in singling out the ideas of space and time and of causation as peculiarly significant. They had become subjects of general discussion among natural philosophers whose attention had been drawn to some of the same problems by the theory of gravitation. On the one hand, Newton seemed to have banished a priori explanation from natural philosophy, and established experiment as the sole basis for scientific truth; but on the other hand, he used concepts that seemed to have no foundation in sense experience. He had shown that gravitational force acted at a distance without any direct physical contact. But as the scientists of his day regarded “natural” and “mechanical” virtually as synonyms, and believed that a “natural” explanation had to be in terms of particles of matter in motion, Newton seemed to have suggested that matter was moved by a non-material, supernatural force. Moreover, one of his central concepts in the Principia was “absolute space and time” for which he gave no experimental evidence. Newton never discussed the metaphysical status of absolute space and time, but he suggested that it might be the sensorium of the Deity, and sometimes spoke as if it described a reality. Certainly, many of his followers took the reality for granted.

The continental admirers of the experimental method, Leibnitz, Huygens, Bernoulli, declared that Newton had left the straight and narrow path of empiricism and had taken refuge in scholastic, occult qualities to explain natural phenomena. As gravitational force was not given by experience, Newton had made a causal inference that was inadmissible in science. Their suspicions were confirmed by the defenders of religion, who eagerly claimed Newton’s theory as evidence for the existence of an immaterial mind and welcomed the notions of “absolute time and space” as proof of man’s ability to discover realities beyond experience, to grasp “occult qualities,” and therefore to know God. Or else, like Clarke, the pious saw a direct relation between infinite space and infinite intelligence.¹ Newton himself preferred “to avoid all questions about the nature or quality of this force,” insisting that he had merely described what he had observed, and did not pretend to explain it. He was sufficiently disturbed by the dangerous implications, however, to try, unsuccessfully, to explain gravitation by means of an ethereal fluid.

Certainly, in the context of mechanically oriented science, both of Newton’s concepts carried intimations of divinity. They moved his contemporaries to consider whether science had to go beyond experience and have recourse to metaphysical realities to explain natural phenomena. They brought into question the whole nature and validity of the causal inference and of abstract ideas.

Hume’s explanation of space and time followed the lines suggested by Newton’s critics. Leibnitz, as well as Toland, argued that time and space were not absolute realities but were meaningful only in connection with objects either coexisting or in succession. We do not understand the manner of the existence of objects in these two distinct ways, they said. We simply find ourselves aware of certain relations of situation or an order of objects. This solution was especially satisfactory for Hume because it enabled him also to reduce the notion of infinity to a similar status. For had he instead resolved space and time into sensation, it would have been at the cost of giving reality to the even more dangerous idea of an infinite being.

That he was mainly concerned to undermine the dependence of abstract ideas on creative reason (without, however, denying their basis in reality), he made perfectly clear. In the first book of the Treatise, he had taken over Berkeley’s criticism of abstract ideas and shown that they were “in themselves individual, however they may become general in their representation. The image in the mind is only that of a particular object, tho’ the application of it in our reasoning be the same as if it were universal.”² But he took Berkeley’s analysis one step further and explained how a particular idea came to stand for other resembling particular ideas. This was, he said, the result of a custom of associating a whole number of objects with the name of one of them: “The word raises up an individual idea, along with a certain custom; and that custom produces any other individual for which we may have occasion.”¹ His hypothesis, Hume declared, was utterly “contrary to that, which has hitherto prevail’d in philosophy.” It was founded on the impossibility of general ideas, as usually understood.

We must certainly seek some new system on this head, and there plainly is none beside what I have propos’d. If ideas be particular in their nature, and at the same time finite in their number, ’tis only by custom they can become general in their representation, and contain an infinite number of other ideas under them.²

His analysis of space and time was entirely parallel to his analysis of abstract ideas, and he carefully underscored the connection. Space and time, as separate realities, were conceived of, he explained, by the imagination. We perceive only patches or points of colour and touch. After experiencing many such coexistences, we can separate the space of these different perceptions from them and think of space in the abstract. The idea of time, because it was derived from a number of different kinds of impressions, afforded, he said, “an instance of an abstract idea which comprehends a still greater variety than that of space, and yet is represented in the fancy by some particular idea of a determinate quantity and quality.”³ The conception of space and time is exactly like the conception of relations, substances and universals. In all these cases, we are misled into turning the fixed names for relations into absolute entities. Such indefinite application of ideas which are originally relative to certain limited perceptions is characteristic of the human mind. It is the work of imagination, and is the result of custom.

As Hume came to recognize in the course of the Treatise, the custom from which, he had said, abstract ideas arise must itself be dependent on a capacity to form general concepts and to make “distinctions of reason” between, for instance, figure and colour, motion and the body moved. It was a difficulty that haunted his whole enterprise—in order to explain how a general term comes to be applied, or how it comes to be, he had to allow that the mind could recognize the identity of an object through time and could apprehend a resemblance between particular images. Indeed, if a particular idea becomes general by being annexed to a general term, the recognition of a resemblance between particulars must occur before that use of the general term upon which the custom rests. How these operations were possible to a mind whose every idea is derived from an impression, Hume never explained. He merely took the relation of resemblance for granted as an ultimate fact of experience. Philosophers have since suggested that he might have escaped these difficulties by acknowledging and developing a supplementing and synthetic activity of the imagination at which he hints. But he could not have gone much further than he did without running a danger he was most anxious to avoid, of letting in by another door the kind of power he was trying to exclude.

Custom played an even more remarkable role in Hume’s theory of causation. And far from denying the radicalism of his theory, he made certain his readers noticed that the notion of causality was at the heart of all discussions of human intelligence and that his views were most unorthodox:

I doubt not but these consequences will at first sight be receiv’d without difficulty, as being evident deductions from principles, which we have already establish’d, and which we have often employ’d in our reasonings. This evidence … may seduce us unwarily into the conclusion, and make us imagine it contains nothing extraordinary, nor worthy of our curiosity … for which reason I think it proper to give warning, that I have just now examin’d one of the most sublime questions in philosophy, viz., that concerning the power and efficacy of causes, or that quality which makes them be followed by their effects. ”¹

Hume had no wish to deny that there was a real connection between cause and effect or that all our reasoning depended on our being convinced that the connection was a necessary one. Quite the contrary, the very necessity of the causal relation was crucial for his purpose. That cause and effect were connected by contiguity and succession, Hume granted at once. But that did not explain, he pointed out, what was really distinctive about the causal relation, that it seemed to be a necessary connection: “Shall we then rest contented with these two relations of contiguity and succession as affording a compleat idea of causation? By no means. An object may be contiguous and prior to another without being considered its cause. There is also a necessary connexion to be taken into consideration.”² We can see that the dog moves and that the stone does not; we see the facts and can conceive of their contrary; yet we say that the dog must move and the stone can not. In the same way, we do not say simply that every change has a cause, but that it must have a cause. What gives us assurance of that necessity?

If the traditional answer that the necessity is seen by reason, by an intuitive insight into the nature of the cause or of the effect were correct, Hume argued, we should be able to see causal necessity from one instance. We could then say that it was impossible for the one object not to follow, or be conceived not to follow. But in fact, we can conceive of causes and their effects as unconnected, and what is even more important, we never conclude that there is a causal connection until we have seen the same events related in the same way a number of times. As there is nothing in several instances repeated that there is not in any one of them, it cannot be that anything within the objects gives rise to the idea of necessity.¹ The cause must then lie in the mind, not in the objects:

Tho’ the several resembling instances which give rise to the idea of power have no influence on each other, and can never produce any new quality in the object … yet the observation of this resemblance produces a new impression in the mind, which is its real model. … Necessity, then, is the effect of this observation, and is nothing but an internal impression of the mind, or a determination to carry our thoughts from one object to another.²

The necessity assumed is not, and cannot be, a necessity of reason (i.e., intuitively or demonstratively understood); it is only a necessity of feeling, in short, a belief, and it arises from custom.

Hume thus reduced what had formerly been described as an intuition about the essence of things to nothing more exalted than an experience of a customary conjunction between two objects. Again, he was involved in the difficulty that afflicted his analysis of abstract ideas. He did not explain what enabled the mind to recognize “like” causes, or customary conjunctions. If, in fact, we can know only what we have already experienced, how can we depart from experience to recognize an object’s similarity to the one we have experienced in the past? But Hume’s attention was concentrated on what he was denying, that the causal inference was an operation of reason enabling man to discover the rational pattern imprinted on nature by the Divine Mind. Having shown that merely custom explained the feeling of necessary connection between cause and effect, Hume left “those who delight in the discovery and contemplation of ‘final causes,’ “ to “employ their wonder and admiration” elsewhere.¹ He had also eliminated the supposed difference between “moral” and “physical” necessity, for he had shown that all necessity lay in the mind, and arose from the influence of the repeated, constant conjunction of two objects. Instead of necessity there was only chance, reduced to order by custom.²

He had demonstrated, Hume felt, that reasoning never gives rise to “a new original, simple idea,”³ that nowhere in man is there anything “like this creative power, by which it raises from nothing a new idea, and with a kind of Fiat, imitates the omnipotence of its Maker. ”.”⁴ It seemed that human thought possessed unbounded liberty and power, but closer examination revealed that it is “confined within very narrow limits,”

and that all this creative power of the mind amounts to no more than the faculty of compounding, transposing, augmenting, or diminishing the materials afforded us by the senses and experience. … In short, all the materials of thinking are derived either from an outward or inward sentiment; the mixture and composition of these belongs alone to the mind and will.⁵

The implications for the activity of philosophizing were not comfortable. By reducing reason to a combination of imagination and sense impressions, Hume had made it impossible to say why what we believe is true, or in any way to establish the certain validity of our beliefs. He had described the workings of the mind, but in doing so had merged logic with psychology; his description of the causal relationship had made it impossible to explain it. Most awkward of all, his method had not accounted for his own philosophizing. The picture he had drawn of the limitations of human knowledge ruled out his own ability to construct it. He had in fact disproved his tide to prove or disprove anything. His Treatise could only be a miracle, unrelated to the rest.

It had not, however, been an interest in discovering the nature of knowing, for its own sake, that had driven him into philosophy. The point of his argument was moral, rather than epistemological, and this he made perfectly plain by concluding his analysis of human understanding with a section on the reason of animals.

Having demonstrated how the human operation that had hitherto been traced to a spiritual power, reason, was no such thing, he then turned the question round. He showed man to be standing closer to the animals than to God, not because, as Hobbes said, man was brutish but because animals were no less spiritual than he. At times Hume almost paraphrased Montaigne to argue that insofar as men reasoned, animals did too. It had long been observed, he said, that animals behaved very much as men did, and that they adapted means to ends in the same manner. It was only natural to assume that the causes of similar behaviour were similar:

We are conscious that we ourselves in adapting means to ends are guided by reason¹ and design, and that ’tis not ignorantly nor casually we perform those actions, which tend to self-preservation, to the obtaining pleasure and avoiding pain. When therefore we see other creatures, in millions of instances perform like actions, and direct them to like ends, all our principles of reason and probability carry us with an invincible force to believe the existence of a like cause. … The resemblance betwixt the actions of animals and those of men is so entire in this respect, that the very first action of the first animal we shall please to pitch on, will afford us an incontestable argument for the present doctrine.²

Hume pointed out that this was not just a parenthetical observation but at the heart of his argument—“This doctrine is as useful as it is obvious, and furnishes us with a kind of touchstone, by which we may try every system in this species of philosophy.”³ It is easy, he declared, to test any hypothesis advanced to explain a mental operation by asking whether it applies equally well to men and beasts. Other philosophical systems supposed “a subtilty and refinement of thought” in a degree that exceeded the capacities not only of animals but also of most human beings. His own system, however, could “equally account for the reasonings of beasts as well as for those of the human species.” And it was the only philosophical system that could. Since it is generally admitted that beasts do not perceive any real connection among objects, or form any general conclusions, yet learn from experience and adapt their behaviour accordingly, it is evident that “rational” behaviour does not depend on reason in the sense given it by philosophers: “I assert they [rational actions of animals] proceed from a reasoning, that is not in itself different, nor founded on different principles from that which appears in human nature.”¹

Here perhaps Hume was more artful than candid. The force of his argument about animals is certainly that if we do not need to postulate a creative reason in order to explain the behaviour of animals, we need not do so for humans. But he avoided making an offensive statement by reversing the order, and declaring that, “All this was sufficiently evident with respect to man. But with respect to beasts there cannot be the least suspicion of mistake; which must be own’d to be a strong confirmation, or rather an invincible proof of my system.”² Hume was tactful, but his meaning is clear. Was it not odd, he asked, that men took their own reason for granted, but were astonished by the instinct of animals? It was only because they had not been able to reduce animal instinct to the same principles. In the light of his new philosophy, however, the problem vanished, because it removed the apparent distinction between human reason and animal instinct. It discovered reason to be “nothing but a wonderful and unintelligible instinct in our souls which carries us along a certain train of ideas, and endows them with particular qualities, according to their particular situations and relations.” It was an instinct that resulted from habit, and “habit is nothing but one of the principles of nature and derives all its force from that origin.”³ Man, then, was not outside or beyond nature, but part of it, merely a more elaborate animal: “Everything is conducted by springs and principles, which are not peculiar to man, or any species of animals.”⁴ Montaigne’s essays had been given a metaphysical foundation.

That Hume had done something radical, all his contemporaries sensed. What the radicalism consisted in, however, they did not quite grasp. Only Kant recognized the full implications of Hume’s theory. He saw the import of Hume’s concentration on the “necessity” of the causal relation, that he had denied not the reality of causation or the necessity of reasoning in the ordinary way, but rather the existence of “pure reason.” As Hume had reduced reason to nature, Kant hoped to save reason by divorcing it from nature more thoroughly than anyone had yet dared. He purified reason of its traditional character as pupil, receiving what nature chose to give, and transformed it into a judge, “who compels the witnesses to reply to those questions which he himself thinks fit to propose.”¹ Thus Kant put the defence of creative reason on a totally new footing, which was, he hoped, not so vulnerable as Hume had shown the old one to be.

If one accepted Hume’s picture of human nature, the whole hierarchy of being was rearranged. The Treatise proposed a metaphysics that was profoundly subversive of the Christian outlook. It was no wonder that Hume’s friends wished him to withhold from publication his Dialogue on Natural Religion, and that he should have taken such great pains to insure its appearance after his death. For the Dialogue stated the postulate upon which the Treatise was based in its most general and simple form.

The general question of how mind and matter were related had interested Hume from the beginning. He had studied Bayle’s account of Strato’s atheism and Cicero’s Dialogue of the Nature of the Gods, and was curious about the Cartesian philosophy of the brain. He had noticed throughout the history of philosophy that the most prevalent views had driven a sharp line between matter and spirit. Either they took up an atomistic, materialist position, like that of Epicurus, Democritus, Leucippus, and asserted that there was nothing but senseless matter and chance, or else they insisted that nature could not be explained without adding a spiritual, ordering force beyond matter. There was, however, a third possibility, suggested by Strato, and discussed by Cicero, that order is somehow inherent in matter. Strato’s atheism was “the most dangerous of the ancient, holding the origin of the world from nature or a matter endowed with activity,” Hume remarked in his notes.² What he himself had decided, he made plain in the Dialogues Concerning Natural Religion.

Thought is not the only principle of order disclosed in experience, he pointed out. There are an infinite number of springs and principles which even our limited knowledge of nature shows her to possess—heat and cold, attraction and repulsion, instinct and generation. We know that every part of nature has its own life and motion, which not only operates it, but coordinates it with the whole. Our experience would seem to deny the possibility of matter utterly devoid of order, or, even spirit without matter. Certainly in all instances that we know, thought can influence matter only when it is joined to it, and it can be as easily influenced by matter. We have no reason to make “this little agitation of the brain” the model of the universe.³

Besides, as we constantly see reason arise from generation, never generation from reason, we might more easily make generation the principle of order than reason. It is no less intelligible or compatible with experience to say that the world arose by vegetation from a seed, than to say that it arose from a divine reason or contrivance.¹ An orderly system might as easily have been spun from the belly of an infinite spider as from a mind. Reason itself is no more intelligible than any other ordering principle: “But reason, in its internal fabric and structure, is really as little known to us as instinct or vegetation; and perhaps even that vague, undeterminate word, nature, to which the vulgar refer everything is not at bottom more inexplicable.”²

In the Dialogue, no one of the disputants gains a victory, although no one really refutes Philo’s statement:

For aught we can know a priori, matter may contain the source or spring of order originally within itself, as well as mind does; and there is no more difficulty in conceiving, that the several elements from an internal unknown cause, may fall into the most exquisite arrangement, than to conceive that their ideas, in the great universal mind, from a like internal unknown cause, fall into that arrangement. The equal possibility of both these suppositions is allowed.³

The emphasis falls not so much on any particular theory, as on denying the possibility of knowing what either matter or mind is, or precisely how the universe is arranged: “These words, generation, reason, mark only certain powers and energies in nature, whose effects are known but whose essence is incomprehensible; and one of these principles, more than the other, has no privilege for being made a standard to the whole of nature.”⁴ The sum of Hume’s argument is that by experience we know that there is an order in nature, but we cannot know how it comes to be. It is therefore presumptuous to try to distinguish matter from mind, to say that one lacks order and the other imposes it. The very distinction is beyond our capacities. Even Father Malebranche, he pointed out, considered it blasphemous to call God a spirit, and argued that He was neither spirit nor matter, but simply, “ ‘He that is,’ or, in other words, Being without restriction, all Being, the Being infinite and universal.”¹ It was far better to rest with a more modest theory, and ascribe “an eternal inherent principle or order to the world, though attended with great and continual revolutions and alterations.” This, by being so general, solved all difficulties; it was perhaps “not entirely complete and satisfactory,” but it was at least a “theory that we must sooner or later, have recourse to, whatever system we embrace.”² For we know only that “everything is surely governed by steady inviolable laws.” If we could know the “inmost essence of things,” we would then “discover a scene, of which, at present we can have no idea.”³

Hume preferred to leave the various arguments in his dialogue more or less in balance, not merely because he might thereby avoid offending popular opinion, but because, above all, he wanted to say that in the end we can but acknowledge a mystery. Neither spirit nor matter was to be made supreme. He had indeed attacked the argument from design, that argument for God’s existence which the faithful regarded as the very heart of religion. And yet he was not an atheist strictly speaking, but a true defender of religion in its most generic meaning, as a sense of wonder. For he insisted that understanding the order of the universe was not within man’s power:

The whole is a riddle, an aenigma, an inexplicable mystery. Doubt, uncertainty, suspence of judgement appear the only result of our most accurate scrutiny, concerning this subject. But such is the frailty of human reason, and such the irresistible contagion of opinion, that even this deliberate doubt could scarcely be upheld; did we not enlarge our view, and opposing one species of superstition to another, set them a quarrelling; while we ourselves, during their fury and contention, happily make our escape into the calm, though obscure regions of philosophy.¹

Hume had used the “experimental method” not to confirm but to thwart the scientific spirit. For the scientist, however much he may assert that he wishes merely to observe the phenomena of this world, however much he denies the possibility of explaining them, is driven by the momentum of his own work into attempting to discover all or believing he could. He may say that his general laws describe nothing real, but even if he himself refrains from doing so, his disciples, as Newton’s did, will take the reality of his scientific laws for granted. But Hume not only insisted on a fundamental, impenetrable mystery; he not only disintegrated the very power that was supposed to give men access to certain and undeniable truth. He denied also the sort of world that the scientists, from Copernicus on, had been creating.

Although insofar as he expelled formal and final causes Hume spoke for the new experimental science, in another way he was behind his time. On the one hand, he admired Newton for the wrong reasons: “While Newton seemed to draw off the veil from some of the mysteries of nature, he showed at the same time the imperfections of the mechanical philosophy; and thereby restored her ultimate secrets to that obscurity in which they ever did and ever will remain.”² On the other hand, despite his criticism of “the mechanical philosophy,” Hume had taken his stand with Newton’s opponents who refused to accept a mathematical force. He used Newton’s own method to declare himself against the timeless world of immaterial forces that Newton, in completing the world view of the new science, proposed to substitute for a simpler, mechanical world, where men did not venture beyond everyday experience. The effect of Newtonism was to abolish the world of more or less, of qualities and sense perception, of concentration on our daily life, and to replace it by an Archimedean universe of precision, of quantity, and rest, where there is a place for everything but humanity. It substituted a mathematical nature for a physical nature, a world of being for a world of becoming and change. It reduced motion from a process of change that affected bodies and differed from rest to a status as permanent and indestructible as rest. Motion became a changeless change in a timeless time. It was no longer the motion of daily experience.

But Hume, as a philosopher of becoming, not of being, preferred the world he could feel about him to the Platonic idea of a mathematical world. His standpoint was more nearly that of the artist than of the philosopher—he was more concerned to remember the particular experiences behind abstract ideas than to organize experience under concepts. In the world as he saw it, all qualities are mixed and confused; there are no distinctions of kind, but only of degree: “Nothing in this world is perpetual; Every thing, however seemingly firm, is in continual flux and change.”¹