Certainly, if any devout Arnoldian says that Diderot’s greatness is due to his “fertility in ideas,” no contradiction will be thought of here. But then we have the old difficulty as to what “ideas” mean. I do not remember that Mr Arnold himself makes much reference to our Denis; and, indeed, Diderot must have been, from some points of view, nearly as horrible—let us lay cards on table and say as incomprehensible—to him as to his friend M. Scherer. But it may be that the critical “idea” is neither more nor less than the result of that contact of subject and critic which has been glanced at before—a contact intimate, physical, uninterrupted, and resulting in conception and birth. This, if anything, is the “idea” of modern criticism; and while few have been more prolific of such results than Diderot, none before him and hardly any since have so invariably and consciously guided themselves by its law. I do not know that he has ever positively stated this law; I really do not know that it ever has been explicitly laid down by any of the constituted, or even the non-constituted, critical authorities. But his whole work is an exemplification of it. And the result is, that this whole work, wherever it approaches criticism, is alive; and that he cannot help its becoming alive, even if he has apparently given hostages to Death by attempting set dissertations on cut-and-dried subjects, or by dallying with science, or atheism, or what not. It is a further reason why even such contemporaries as Lessing, and later, Goethe, found in him such an extraordinary stimulus. The dead, mechanical deductions of too many critics under the older system could produce nothing but copies, even more dead and more mechanical than themselves, though, as we have seen in many a figure of our gallery, the principle of life in human nature made the greater critics of the older dispensation sometimes quicken under it. But Diderot’s fecundity was contagious: his “cultures” have propagated themselves from generation to generation directly, have set the example of a similar creation of critical entities to fit subjects ever since. From a formula you will never get anything but formulas: from the living contact of critic and subject you will get live criticism. [Sidenote: _Rousseau revisited._]