10. Of the bearing of this view on the question at issue between Mr. Mill and me, I may hereafter speak; but I will now notice other persons who have misunderstood me in the same way.
An able writer in the Edinburgh Review[312] has, in like manner, said, "Dr. Whewell seems to us to have gone much too far in reducing to necessary truths what assuredly the generality of mankind will not feel to be so." It is a fact which I do not at all contest, that the generality of mankind will not feel the Axioms of Chemistry, or even of Mechanics, to be necessary truths. But I had said, not that the generality of mankind would feel this necessity, but (in a passage just before quoted by the Reviewer) that the mind under certain circumstances attains a point of view from which it can pronounce mechanical (and other) fundamental truths to be necessary in their nature, though disclosed to us by experience and observation.
Both the Edinburgh Reviewer and Mr. Mansel appear to hold a distinction between the fundamental truths of Geometry, and those of the other subjects which I have classed with them. The latter says, that perhaps metaphysicians may hereafter establish the existence of other subjective conditions of intuitions (or, as I should call them, Fundamental Ideas,) besides Space and Time, but that in asserting such to exist in the science of Mechanics, I certainly go too far: and he gives as an instance my Essay,—"Demonstration that all matter is heavy." I certainly did not expect that the Principles asserted in that Essay would be assented to as readily or as generally as the Axioms of Geometry; but I conceive that I have there proved that Chemical Science, using the balance as one of its implements, cannot admit "imponderable bodies" among its elements. This impossibility will, I think, not only be found to exist in fact, but seen to exist necessarily, by chemists, in proportion as they advance towards general propositions of Chemical Science in which the so-called "imponderable fluids" enter. But even if I be right in this opinion, to how few will this necessity be made apparent, and how slowly will the intuition spread! I am as well aware as my critics, that the necessity will probably never be apparent to ordinary thinkers.
11. Though Mr. Mansel does not acknowledge any subjective conditions of intuition besides Space and Time, he does recognize other kinds of necessity, which I should equally refer to Fundamental Ideas; because they are, no less than Space and Time, the foundations of universal and necessary truths in science. Such are[313] the Principle of Substance;—All Qualities exist in some subject: and the Principle of Causality;— Every Event has its Cause. To these Principles he ascribes a "metaphysical necessity," the nature and grounds of which he analyses with great acuteness. But what I have to observe is, that whatever differences may be pointed out between the grounds of the necessity, in this case of metaphysical necessity, and in that which Mr. Mansel calls mathematical necessity which belongs to the Conditions or Ideas of Space and of Time; still, it is not the less true that the Ideas of Substance and of Cause, do afford a foundation for necessary truths, and that on these truths are built Sciences. That every Change must have a Cause, with the corresponding Axioms,—that the Cause is known by the Effect, and Measured by it,—is the basis of the Science of Mechanics. That there is a Substance to which qualities belong, with the corresponding Axiom,—that we cannot create or destroy Substance, though we may alter Qualities by combining and separating Substances,—is the basis of the Science of Chemistry. And that this doctrine of the Indestructibility of Substance is a primary axiomatic truth, is certain; both because it has been universally taken for granted by men seeking for general truths; and because it is not and cannot be proved by experience[314]. So that I have here, even according to Mr. Mansel's own statement, other grounds besides Space and Time, for necessary truths in Science.
12. Besides mathematical and metaphysical necessity, Mr. Mansel recognizes also a logical necessity. I will not pretend to say that this kind of necessity is exactly represented by any of those Fundamental Ideas which are the basis of Science; but yet I think it will be found that this logical necessity mainly operates through the attribution of Names to things; and that a large portion of its cogency arises from these maxims,—that names must be so imposed that General Propositions shall be possible,—and so that Reasoning shall be possible. Now these maxims are really the basis of Natural History, and are so stated in the Philosophy of the Inductive Sciences. The former maxim is the principle of all Classification; and though we have no syllogisms in Natural History, the apparatus of genus, species, differentia, and the like, which was introduced in the analysis of syllogistic reasoning, is really more constantly applied in Natural History than in any other science.
13. Besides the different kinds of necessity which Mr. Mansel thus acknowledges, I do not see why he should not, on his own principles, recognize others; as indeed he appears to me to do. He acknowledges, I think, the distinction of Primary and Secondary qualities; and this must involve him in the doctrine that Secondary Qualities are necessarily perceived by means of a Medium. Again: he would, I think, acknowledge that in organized bodies, the parts exist for a Purpose; and Purpose is an Idea which cannot be inferred by reasoning from facts, without being possessed and applied as an Idea. So that there would, I conceive, exist, in his philosophy, all the grounds of necessary truth which I have termed Fundamental Ideas; only that he would further subdivide, classify, and analyse, the kinds and grounds of this necessity.
In this he would do well; and some of his distinctions and analyses of this kind are, in my judgment, very instructive. But I do not see what objection there can be to my putting together all these kinds of necessity, when my purpose requires it; and, inasmuch as they all are the bases of Science, I may call them by a general name; for instance, Grounds of Scientific Necessity; and these are precisely what I mean by Fundamental Ideas.
That some steady thought, and even some progress in the construction of Science, is needed in order to see the necessity of the Axioms thus introduced, is true, and is repeatedly asserted and illustrated in the History of the Sciences. The necessity of such Axioms is seen, but it is not seen at first. It becomes clearer and clearer to each person, and clear to one person after another, as the human mind dwells more and more steadily on the several subjects of speculation. There are scientific truths which are seen by intuition, but this intuition is progressive. This is the remark which I wish to make in answer to those of my critics who have objected that truths which I have propounded as Axioms, are not evident to all.
14. That the Axioms of Science are not evident to all, is true enough, and too true. Take the Axiom of Substance:—that we may change the condition of a substance in various ways, but cannot destroy it. This has been assumed as evident by philosophers in all ages; but if we ask an ordinary person whether a body can be destroyed by fire, or diminished, will he unhesitatingly reply, that it cannot? It requires some thought to say[315], as the philosopher said, that the weight of the smoke is to be found by subtracting the weight of the ashes from that of the fuel; nay, even when this is said, it appears, at first, rather an epigram than a scientific truth. Yet it is by thinking only, not by an experiment, that, from a happy guess it becomes a scientific truth. And the thought is the basis, not the result, of experimental truths; for which reason I ascribe it to a Fundamental Idea. And so, such truths are the genuine growth of the human mind; not innate, as if they needed not to grow; still less, dead twigs plucked from experience and stuck in from without; not universal, as if they grew up everywhere; but not the less, under favourable circumstances, the genuine growth of the scientific intellect.
15. Not only do I hold that the Axioms, on which the truths of science rest, grow from guesses into Axioms in various ways, and often gradually, and at different periods in different minds, and partially, even in the end; but I conceive that this may be shown by the history of science, as having really happened, with regard to all the most conspicuous of such principles. The scientific insight which enabled discoverers to achieve their exploits, implied that they were among the first to acquire an intuitive conviction of the Axioms of their Science: the controversies which form so large a portion of the history of science, arise from the struggles between the clear-sighted and the dimsighted, between those who were forwards and those who were backwards in the progress of ideas; and these controversies have very often ended in diffusing generally a clearness of thought, on the controverted subject, which at first, the few only, or perhaps not even they, possessed. The History of Science consists of the History of Ideas, as well as of the History of Experience and Observation. The latter portion of the subject formed the principal matter of my History of the Inductive Sciences; the former occupied a large portion of the Philosophy of the Inductive Sciences[316]; which, I may perhaps be allowed to explain, is, for the most part, a Historical Work no less than the other; and was written in a great measure, at the same time, and from the same survey of the works of scientific writers.