What Are Laws Of Nature?
78. REFERRING to what was briefly stated in our Inroduction (On the Method of Science, § 70 et seq.), we there saw that Law was originally supposed to have not only an objective existence in the phenomena, but an objective existence independent of the phenomena ; and this ancient error is still alive. By one of the illusions into which Philosophy easily glides, a Law of Nature is supposed to hold a position with respect to natural objects which is analogous to that held by a legislative enactment with respect to social life. Laws are a kind of wise police keeping Nature in order. How far the connotations of Language inevitably transfer this conception of the regulation of conduct to the regulation of Nature, it may be difficult to say ; but the fact is that, having once named Process by the word Law, we have great difficulty in keeping the two conceptions distinct. Even careful writers are apt to express themselves ambiguously on this point ; and the majority of writers assuredly suppose that Law is independent of the phenomena which it rules. Strongly impressed with the mischievous tendency of its suggestions, I was many years ago led to propose the abandonment of the word Law in relation to physical phenomena ; but I soon found that the reform was impracticable; the word is too deeply rooted. Instead, there-fore, of attempting to get rid of it, we must be content with a recognition of its misleading connotations, and fix in our minds that Law is only one of two conceptions, 1°, a notation of the process observed in the phenomena, which process we mentally detach and generalize by ex-tending it to all similar phenomena ; 2°, an abstract Type, which although originally constructed from the observed Process, does nevertheless depart from what is really observed, and substitutes an Ideal Process, constructing what would be the course of the process were the conditions different from those actually present.
79. The first conception is so far real that it expresses the observed series of positions. It is the process of phenomena, not an agent apart from them, not an agency determining them, but simply the ideal summation of their positions. The story of a man's life is not a theorem which he has to work out, but a story which we elicit from all the events, and exhibit in its leading directions. Phenomena, in as far as they are ruled, — regulated, determined in this direction rather than in that, and necessarily determined in the direction taken, — are determined by no external agent corresponding to Law, but by their co-operant factors internal and external : alter one of these factors, and the product will be differently determined.
It is owing to the very general misconception of the nature of Law that there arise the misconception of Necessity ; the fact that events arrive irresistibly when-ever their conditions are present, is confounded with the conception that the events must arrive whether the conditions be present or not, being fatally predetermined. Necessity simply says that whatever is is, and will vary with varying conditions. Fatalism says that something must be ; and this something cannot be modified by any modification of the conditions.
Every Law has two aspects, one concrete and experimental, the other abstract and theoretical. In the experimental department a Law is simply the notation of observed facts ; in the theoretical department this is exhibited as the necessary consequence of certain other and more fundamental facts ; and, as Prof. Challis reminds us, " every fact, every law which experiment makes known, is a problem for the theorist to solve by mathematical reasoning." Kepler discovered that the radius vector of each planet would describe round the sun equal areas in equal times, were there no perturbing conditions ; and he grouped the, observed facts under this Law. Then came Newton, who deduced this Law, not from the observed facts, but from the primary fact of which it was the necessary consequence, namely, the Law that gravitation is a' force acting in the line of the attracting and attracted bodies.
80. A Real Law differs from an Ideal Law, or Type, not in being less of a subjective conception, but in being less of a construction, — not in having an existence independent of objects and of us, in contradistinction to the Ideal Law supposed to be entirely our own creation, but in expressing more rigorously the. results of observation, and being thus reducible to sensible experience. It so far agrees with the Type that it is not any one series of observed positions, but a generalized series, — an abstract group of resemblances from which differences are rejected. By this generalization a particular series becomes a general Law, under which all resembling phenomena are classed, and the notation is made once and forever. We are said to have explained any particular fact when we have ranged it under the series to which it belongs, in other words, assigned its Law. What is this ? simply the series of positions which each phenomenon occupies under definite conditions. The position is not determined by the series ; the phenomenon is not coerced by the Law, but each successive position is assumed be-cause that, and no other, is the resultant of the co-operant forces. And when observation discloses a discrepancy between a fact and its Law, do we not at once declare this to be due to some difference in the factors ? do we not preserve the integrity of the Law by invoking the presence of some perturbation ? Now this is clearly the substitution of one series for another. Perturbations are mere figments of the mind, cloaks for ignorance, unless we acknowledge them to be positions which we do not observe, and which if observed would reveal that this series was not the series expressed in our Law. For in truth the so-called inviolability of Law is absolute only in so far as whatever is is, and cannot be otherwise. It declares the facts to be unchangeable so long as their factors are unchanged.
"Every process," we are told, "has laws known or unknown, according to which it must take place." I regard this as very inexact or very misleading. The law is the process ; and there is no other must in the case than is involved in the identical proposition that the process must be the process. When comets are said to have laws in obedience to which they return at the times predicted, this obedience is metaphorical ; the comets, in fact, some-times do not " obey " the prescribed law, the prediction is falsified because the positions have been different. If it be replied that this only proves our conception of the process to have been inaccurate, and that we neglected in our formula certain elements which were co-operant, this, although perfectly true, only restates the argument that the real law of cometary movement is the series of cometary positions ; and this must in each case be what it is.
81. But if in this sense the Real Law is inviolable because it is simply the expression of what is, and all the so-called perturbations are different Laws, the Ideal Law is of course inviolable, because it is abstracted not only from all perturbations but from all real processes. It ex-presses not what is, but what would be under other conditions. Motion never is uniform, never rectilinear ; the stamen or pistil of a plant never is a leaf the bones of a skull never are vertebræ ; the planet never does describe an ellipse, — these and all other Ideal Laws are abstract truths ; and they can only be applied in explanation of concrete facts by a constant rectification of our natural tendency to mistake abstractions for realities.
82. The distinction here established is not quite the same as that proposed by Mr. Mill, who divides laws into Ultimate and Derivative. He assigns inferior importance to the Derivative Laws, and will not allow them to be Laws of Nature. According to the views exposed in this chapter the Derivative Laws are those understood as Laws of Nature, while the Ultimate Laws are not Laws of Nature, but subjective constructions having no corresponding objects. Mr. Mill holds that the three laws, 1 air has weight ; 2°, pressure on a fluid is propagated equally in all directions ; 3°, pressure in one direction not opposed by equal pressure in the contrary direction produces motion, — are three Laws of Nature. I agree ; but cannot follow him when he adds that although from the combination of these Laws we can predict the rise of mercury in the barometer, this last is not a Law of Nature, but simply a derivation from three Laws, — a case in which all three co-operate. It seems to me that the law of atmospheric gravity is a case of the general law of gravitation, and the law of fluid pressure is not less derivative than that of the rise of mercury in the barometer ; the equal propagation of the pressure is a fact reducible to factors, namely, the uniform disposition of the molecules of the fluid and the laws of motion of those molecules. The only Laws that can with strictness be called ultimate, in Mr. Mill's sense, are those of Number, Position, and Force in the object-world, and those of Sensation and Grouping in the subject-world ; all phenomena may be reduced to cases of these Laws.
83. This mode of regarding Laws, namely, as Processes briefly formulated in their essential characters, and as Types by which Observation may be guided, enables us to escape the fallacy of supposing phenomena to be determined by their own resultants.
Ideal Laws, or Types, stand somewhat in the relation to Real Laws, or Generalization, that Hypotheses do to Theories. There can be no doubt respecting their immense service in Research, and yet they wear the paradoxical aspect of assisting Observation by deliberately neglecting it in favor of Ideal Construction. Before considering the limitations which this employment of Ideal Construction demands, it will be needful here to come to a distinct understanding on the use of hypothesis.
( Originally Published 1874 )
Problems of Life and Mind:
The Reality Of Abstractions
Ideal Construction In Science
What Are Laws Of Nature?
The Use And Abuse Of Hypothesis
The Passage From The Abstract To The Concrete
Ideal Construction In Metaphysics
The Search After Causes
Intuition And Demonstration
Axioms And Their Validity
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