The Pursuit of Certainty. Shirley Robin Letwin

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СКАЧАТЬ 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 СКАЧАТЬ