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In the first place, it is to be noted that the author of the “Reign of Law” admits that “law,” in many cases, means nothing more than the statement of the order in which facts occur, or, as he says, “an observed order of facts” (p. 66). But his appreciation of the value of accuracy of expression does not hinder him from adding, almost in the same breath, “In this sense the laws of nature are simply those facts of nature which recur according to rule” (p. 66). Thus “laws,” which were rightly said to be the statement of an order of facts in one paragraph, are declared to be the facts themselves in the next.

We are next told that, though it may be customary and permissible to use “law” in the sense of a statement of the order of facts, this is a low use of the word; and, indeed, two pages farther on, the writer, flatly contradicting himself, altogether denies its admissibility.

An observed order of facts, to be entitled to the rank of a law, must be an order so constant and uniform as to indicate necessity, and necessity can only arise out of the action of some compelling force (p. 68).

This is undoubtedly one of the most singular propositions that I have ever met with in a professedly scientific work, and its rarity is embellished by another direct self-contradiction which it implies. For on the preceding page (67), when the Duke of Argyll is speaking of the laws of Kepler, which he admits to be laws, and which are types of that which men of science understand by “laws,” he says that they are “simply and purely an order of facts.” Moreover, he adds: “A very large proportion of the laws of every science are laws of this kind and in this sense.”

If, according to the Duke of Argyll’s admission, law is understood, in this sense, thus widely and constantly by scientific authorities, where is the justification for his unqualified assertion that such statements of the observed order of facts are not “entitled to the rank” of laws?

But let us examine the consequences of the really interesting proposition I have just quoted. I presume that it is a law of nature that “a straight line is the shortest distance between two points.” This law affirms the constant association of a certain fact of form with a certain fact of dimension. Whether the notion of necessity which attaches to it has an a priori, or an a posteriori origin is a question not relevant to the present discussion. But I would beg to be informed, if it is necessary, where is the “compelling force” out of which the necessity arises; and further, if it is not necessary, whether it loses the character of a law of nature?

I take it to be the law of nature, based on unexceptionable evidence, that the mass of matter remains unchanged, whatever chemical or other modifications it may undergo. This law is one of the foundations of chemistry. But it is by no means necessary. It is quite possible to imagine that the mass of matter should vary according to circumstances, as we know its weight does. Moreover, the determination of the “force” which makes mass constant (if there is any intelligibility in that form of words) would not, so far as I can see, confer any more validity on the law than it has now.

There is a law of nature, so well vouched by experience, that all mankind, from pure logicians in search of examples to parish sextons in search of fees, confide in it. This is the law that “all men are mortal.” It is simply a statement of the observed order of facts that all men sooner or later die. I am not acquainted with any law of nature which is more “constant and uniform” than this. But will any one tell me that death is “necessary”? Certainly there is no a priori necessity in the case, for various men have been imagined to be immortal. And I should be glad to be informed of any “necessity” that can be deduced from biological considerations. It is quite conceivable, as has recently been pointed out, that some of the lowest forms of life may be immortal, after a fashion. However this may be, I would further ask, supposing “all men are mortal” to be a real law of nature, where and what is that to which, with any propriety, the title of “compelling force” of the law can be given?