1. _As to Efficient Causes_.--Had Comte contented himself with the assertion that causes lie beyond the field of sensible observation, and that inductive science can not carry us beyond the relations of co-existence and succession among phenomena, he would have stated an important truth, but certainly not a new truth. It had already been announced by distinguished mental philosophers, as, for example, M. de Biran and Victor Cousin.[248] The senses give us only the succession of one phenomenon to another. I hold a piece of wax to the fire and it melts. Here my senses inform me of two successive phenomena--the proximity of fire and the melting of wax. It is now agreed among all schools of philosophy that this is all the knowledge the senses can possibly supply. The observation of a great number of like cases assures us that this relation is uniform. The highest scientific generalization does not carry us one step beyond this fact. Induction, therefore, gives us no access to causes beyond phenomena. Still, this does not justify Comte in the assertion that causes are to us absolutely _unknown_. The question would still arise whether we have not some faculty of knowledge, distinct from sensation, which is adequate to furnish a valid cognition of cause. It does not by any means follow that, because the idea of causation is not given as a "physical quæsitum" at the end of a process of scientific generalization, it should not be a "metaphysical datum" posited at the very beginning of scientific inquiry, as the indispensable condition of our being able to cognize phenomena at all, and as the law under which all thought, and all conception of the system of nature, is alone possible. [Footnote 248: "It is now universally admitted that we have no perception of the causal nexus in the material world."--Hamilton, "Discussions," p. 522.]