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the part of common sense, nor reprehensible on the part of science. For it is the primary function of the human mind to discriminate and relate bodies. This function is first in order of practical importance. The human mind, like the heart and lungs, is an organ, calculated to assist the adaptation of one body to an environment of other bodies. This function with reference to other bodies is not only the mind's original function, but remains, during a man's natural lifetime, its most indispensable function. "Our intelligence, as it leaves the hands of nature," says Bergson, "has for its chief object the unorganized solid. When we pass in review the intellectual functions, we see that the intellect is never quite at its ease, never entirely at home, except when it is working upon inert matter, more particularly among solids . . . where our action finds its fulcrum, and our industry its tools." Intelligence is first of all the attentive discrimination of bodies, and a responsiveness to their proximity, motion, or change of property. And when life becomes less preoccupied with its own preservation and more largely engaged in constructive enterprises, it is on its control of its bodily environment that it mainly relies both for security and for power. Science elaborates and perfects this form of intelligence. Through science it becomes methodical and exact. The use of speech and record makes it an institution supported and utilized by society as a whole; its specialization and expansion beyond the demands of present exigencies renders it a means of resourcefulness and initiative.

Common sense and science (the one unconsciously, the other with an increasing degree of consciousness) thus move within the same limits. They share the same unreflective classification of experience, employ the same axes of reference, have the same notion of an individual thing. This is thought's original sin, its inertia and line of least resistance. It is responsible for the sympathy between common sense and science; and for the somewhat strained 1 Creative Evolution, trans. by A. Mitchell, pp. 153-154, ix.

relations between both of these and philosophy, whose business it has ever been to remind them that their favorite assumption is uncritical and dogmatic.

of Bodies

§ 4. We must now attempt a more careful account of that common sense notion of a thing, which is the subjectThe Properties matter to which science addresses itself, and which its terms denote. I have as yet but roughly indicated it by the terms 'body' and 'physical event.' It is not to be expected that either common sense or science should analyze this notion. They analyze one body into lesser bodies, visible bodies into invisible bodies; they distinguish and classify bodies; but they do not attempt to enumerate the generic bodily properties. This is a philosophical task which we must undertake for ourselves.

In describing the unambiguous denotation of the terms of science, I have alluded to gesture and manipulation as means of identification. A body can always be pointed to, or one can 'lay one's hand on it.' Eliminating the accidental human reference, this means that a body has locality, or spacial position. It is somewhere. But when we say 'it is somewhere,' we indicate that the body does not consist of the position alone. There is something which is at the position, or bears to the position the relation of 'occupancy.' Again, it is essential to bodies that they have a history, and thus occupy time as well as space. They are somewhere at some time. The relation of that which occupies space and time, to its spacial and temporal positions, may be either of two kinds. The spacial position may remain the same while the temporal position varies, in which case we speak of a body's being at rest; or the spacial position may vary continuously as the time varies continuously, in which case we speak of motion. Finally, except in the hypothetical case of material points, bodies

1 The best account of the relation of space, time, body, and motion is to be found in B. Russell's writings. Cf. "Is Position in Time and Space Absolute or Relative?" Mind, N.S., Vol. X, 1901; and Principles of Mathematics, Ch. LI, LIII, LIV.

• For the meaning of 'continuous,' cf. Russell, op. cit., Ch. XXIII.

always occupy several positions simultaneously, and accordingly possess spacial extension and figure.

There is a certain convenience in so distinguishing 'body' and 'matter' as to use the term 'body' to mean the distinct individuals of the genus 'matter.' A body is ordinarily regarded as that which moves as a unit; as whatever portion of matter may maintain the mutual positions of its parts unchanged, while their relations to other positions are changed. It is this capacity of an extended unit to be dislocated from its context, which is ordinarily regarded as defining its boundaries. And its identity would then be regarded as unaltered so long as this independence of internal on external relations continued. It is not evident, however, that the possibility of motion is necessary for the definition of an individual body. It is strictly necessary only that a region of space should be marked by some distinguishing character that remains unchanged through time. Matter, or physical being, on the other hand, would mean any complex containing something occupying both space and time. That which occupies space and time is indifferent; it is the space-time occupancy that constitutes its material or physical character. Matter is commonly used also in a narrower but not incompatible sense, to exclude the strictly spacial and temporal properties. In this sense, matter would mean only whatever occupies the space and time, and not the whole complex.

Summarily expressed, then, we may say that 'physical' (bodily or material) connotes two sets of properties: spacial and temporal properties on the one hand; and, on the other hand, space-time-filling properties.2 The former are such as latitude and longitude, shape, date, and motion; the latter such as color, temperature, and sound. The

1 It will, I think, be generally agreed that neither 'hardness' nor even 'impenetrability' is regarded by modern science as an essential property of matter. Cf. Sir Oliver Lodge: Life and Matter, pp. 24-34.

I do not mention the more general logical, arithmetical and algebraic properties, such as 'order,' 'number,' etc., because these are not distinctively physical. See below, pp. 108-109, 310–311.

former may be said to be the fundamental physical properties, because the latter derive their physical character from their relation to the former. It follows that physical events the immediate subject-matter of physical science, are of two general types. There is, first, the change of spacial-temporal properties; and second, the change of spacetime-filling properties: in short, change of place, and change of state. These events it is the task of science to explain. 5. In what sense does science seek to explain'? Explanation is supposed to supply an answer to the question "Why?" But this interrogative pronoun Explanation and Description suggests several questions which, in the course in Science of the development of science, have proved irrelevant to its special interest. For many minds, and, during a considerable period, even for the scientific mind, the demand for explanation has been satisfied by the reference of an event to a power, regarded as sufficient to produce it. Thus before Galileo's time, terrestrial motions were accounted for by attributing them to powers of "gravity" and "levity." And similarly Kepler explained planetary motions by attributing them to celestial spirits.1 It seemed necessary to provide an agency having a capacity for effort as great as, or greater than, the effect; and immediately present to the effect, as the soul is present to the body it moves. But Galileo and Kepler have contributed to the advancement of science only because they have added to such explanation as this, an exact account of the process or form of terrestrial and planetary motions. Just how do bodies fall and planets move? This is the question which for scientific purposes must be answered; and only such answers have been incorporated into the growing body of scientific knowledge. Who or what moves bodies, in the sense of agency or potency, is for scientific purposes a negligible question; attempts to answer it have been, in the course of the development of science, not disproved, but disregarded.

1 Whewell: History of the Inductive Sciences, third edition, Vol. I, p. 315.

And the same is true of another sense of the interrogative 'why.' It is not infrequently taken to mean, "To what end?" "For what good?" Thus, we are said to 'understand' the beneficent works of nature, but to 'see no reason' for vermin, disease, and crime. Or, if we do seek a reason, we find it in some indirect beneficence that may be attributed to these things, despite appearances. This is the teleological or moral type of explanation. It appears in the ancient regard for 'perfect' numbers and forms, in the Platonic principle of the Good, and in the Christian notion of Providence. But this species of explanation, too, has been not disproved, but progressively disregarded by science. It has come to be the recognized aim of science to formulate what happens, whether for better or for worse; leaving out of account, as an extra-scientific concern, whatever bearing it may have on interest.1

It appears, in other words, that the common distinction between explanation and 'mere description' will not strictly hold in the case of scientific procedure. For science, to explain is to describe — provided only that the description satisfies certain conditions."

Conditions of

scription

§ 6. There are two specific conditions which description must fulfil, if it is to be sufficient in the scientific sense. In the first place, scientific description must reveal Scientific De- the general and constant features of its subjectmatter. It is a truism that thought tends to unify. The bare quale of phenomena, their peculiar individuality, gives way to certain underlying identities. Or, since natural science deals primarily with changes, bare novelty gives way to an underlying permanence. In other words, scientific thought is interested in what is the same, despite difference, or in what persists, despite change.3

1 For this purely theoretical motive in science, cf. above, pp. 25-28.

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2 Cf. E. Mach: The Economical Nature of Physical Inquiry" in his Popular Scientific Lectures, trans. by T. J. McCormack, p. 186.

3 As we shall presently see, this does not mean that science forces identity and permanence upon an alien chaos or flux, but only that science is interested in laying bare what identity and permanence is there.

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