But Co-operation, if it neglects Malthus, will find its work no sooner done than undone. It may be thought that there are causes at work which will remove over-population among the working classes even under the present system of separated capital and labour. It is a doctrine of the “finer wits,” founded on striking biological analogies, that the general development of intellect in the race will weaken the passion for marriage and supersede the necessity for any checks on it;[922]—the exercise of the energies of concentration or “individuation” developes these energies at the expense of those of diffusion or “genesis;”—the individual is made strong in himself, at the expense of his power of creating new individuals. Quite apart from the disagreeable fact that this principle would lessen the pressure most in those classes where lessening is at present least needed, and least where it is most needed, Malthus would probably have pointed out, first, that unless the appetite is absolutely killed, no physiological check can supersede some control of the will over the passion,—and, second, that intellectual development will more certainly check population by making men alive to their responsibilities and strengthening their power of restraint than by weakening the passion to be restrained. The expounder of the theory is of all people the least likely to teach men that they may become civilized by the progress of their race without the trouble of civilizing themselves individually. But his theory admits the misapplication; and, if it be said by the misappliers that we ought to tell the truth without fear of consequences, we must answer that in this case the consequences are part of the truth. On the other hand, to theorists like W. R. Greg, who suggest unknown physiological laws that may act as a spontaneous check, Malthus would have replied as to Condorcet:[923] “What can we reason but from what we know?” This brief survey of typical critics and commentators may be completed by a classification of the former, which, among other advantages, will give a bird’s-eye view of the chief points in discussion. Empson classified the opponents of Malthus by their motives,[924] a proceeding hardly fair either to them or to the essay itself. It is not fair to them, for as a rule the critics appeal to argument, and must be judged by what they adduce, not by their good or ill will, wisdom or folly, in adducing it; and not fair to the essay, because few books have owed so much to their reviewers. The positions of the critics may be classified as follows:— I. Some say the doctrine of the essay is a truism.[925] II. Others admit that it is unanswerable, but retain a philosophical faith in the future discovery of some contrary principle.[926]