There is one feature, however, which their general theories of knowledge have in common, and which I must mention--for its own sake as well as because it will give me an opportunity to refer to an interesting question which I shall not have time to consider elsewhere in this chapter: the original source of their common ideas.
The point of their doctrines to which I refer is one on which at first they may appear to hold diametrically opposed views: their attitude to empirical research. For Comte this constitutes the whole of science; for Hegel it is entirely outside what he calls science, although he by no means underrates the importance of factual knowledge within its sphere. What brings them together is their belief that empirical science must be purely descriptive, confined to establishing regularities of the observed phenomena. They are both strict phenomenalists in this sense, denying that empirical science can proceed from description to explanation. That the positivist Comte regards all explanation, all discussion of the manner in which the phenomena are produced, as futile metaphysics, while Hegel reserves it to his idealistic philosophy of nature, is a different matter. In their views on the functions of empirical research they agree almost completely, as Smile Meyerson has beautifully shown.17.19 When Hegel argues, for example, that ``empirical science has no business to assert the existence of anything that is not given to sense preception,''17.20he is as much a positivist as Comte.
Now this phenomenalist approach to the problems of empirical science derives in modern times without question from Descartes, to whom both philosophers are directly indebted. And the same is, I believe, true of the second basic feature which they have in common and which will show up strongly in the more detailed points on which they agree: their common rationalism, or better, intellectualism. It was Descartes who first combined these apparently incompatible ideas of a phenomenalist or sensualist approach to physical science and a rationalist view of man's task and functions.17.21With respect to the points in which we are chiefly interested, it was mainly through Montesquieu,17.22d'Alembert,17.23 Turgot, and Condorcet in France, Herder,17.24 Kant, and Fichte in Germany, that the Cartesian heritage was passed on to Hegel and Comte. But what in those men had been merely bold and stimulating suggestions became with our two philosophers the bases of the two ruling systems of thought of their time. In thus stressing the common Cartesian origin of what I believe to be the common errors of Hegel and Comte, I wish, of course, not in the least to depreciate the great service which Descartes has rendered to modern thought. But as has been true with so many fertile ideas, a stage is often reached when their very success brings about their application to fields in which they are no longer appropriate. And this, I believe, is what Comte and Hegel have done.