An important section of his second Essay, Psychologie rationnelle, deals with the “Classification of the Sciences.”[[23]] Renouvier there points out that the attempt to classify the sciences in accordance with their degrees of certainty ends in failure. All of them, when loyal to their own principles, endeavour to display equal certainty. By loyalty Renouvier shows that he means adherence to an examination of certain classes of phenomena, the observation of facts and laws, with the proposal of hypotheses, put forward frankly as such. He draws a line between the logical and the physical sciences—a division which he claims is not only a division according to the nature of their data, but also according to method. Following another division, we may draw a line between sciences which deal with objects which are organic, living creatures, and those which are not.
[23] Vol. 2, chap. xviii., De la Certitude des Sciences et leur Classification rationnelle, pp. 139-186, including later observations on Spencer.
Renouvier’s line is not, it must be remembered in this connection, a purely imaginary one. It is a real line, an actual gap. For him there is a real discontinuity in the universe. Taine’s doctrine of a universal explanation, of a rigid unity and continuity, is, for Renouvier, anathema, c’est la mathématisation a l’outrance. This appears most markedly in the pages which he devotes to the consideration of la synthèse totale.
An important section of his Traité de Logique (the first Essai de Critique générale) deals with the problem of this Total Synthesis of all phenomena.[[24]] This is a conception which Renouvier affirms to be unwarrantable and, indeed, in the last analysis impossible. A general synthesis, an organisation or connected hierarchy of sciences, is a fond hope, an illusion only of a mind which can overlook the real discontinuity which exists between things and between groups of things.
[24] Vol. I, pp. 107-115, and also vol. 2, pp. 202-245.
He sees in it the fetish of the Absolute and the Infinite and the lure of pantheism, a doctrine to which he opposes his “Personalism.” He reminds the scientists that personality is the great factor to which all knowledge is related, and that all knowledge is relative. A law is a law, but the guarantee of its permanence is not a law. It is no more easy, claims Renouvier, to say why phenomena do not stop than it is to know why they have begun. Laws indeed abide, but “not apart from conscious personalities who affirm them.”[[25]] Further, attacking the self-confident and dogmatic attitude in the scientists, Renouvier reminds them that it is impossible to demonstrate every proposition; and in an important note on “Induction and the Sciences”[[26]] he points out that induction always implies a certain croyance. This is no peculiar, mystical thing; it is a fact, he remarks, which colours all the interesting acts of human personality. He here approaches Cournot in observing that all speculation is attended by a certain coefficient of doubt or uncertainty and so becomes really rational belief. With Cournot, too, Renouvier senses the importance of analogy and probability in connection with hypotheses in the world of nature and of morals. In short, he recognises as central the problem of freedom.
[25] Logique, vol. 2, p. 321.
[26] Note B to chap. xxxv. of the Logique, vol. 2, p. 13.
Renouvier attacks Comte’s classification or “hierarchy” of the sciences as mischievous and inexact. It is not based, he claims, upon any distinction in method, nor of data. It is not true that the sciences are arranged by Comte in an order where they successively imply one another, nor in an order in which they have come to be constituted as “positive”.[[27]]
[27] This outburst of attack is a sample of Renouvier’s usual attitude to Positivism. (Deuxième Essai, vol. 2, pp. 166-170.)