To begin with the subjective side. It may be thought that we can point to some impulse, tendency, motive, or class of motives in the individual mind by following which the evolution of life will be promoted, and that we are thus able to solve the question of practical ethics, though our conception of what the evolution of life connotes may still be in want of exact definition. As already pointed out, such an impulse (unless it depends on an objective standard) must carry its own authority with it by its strength or persistency. The case would, of course, be perfectly simple, if we could assert that the carrying out of all impulses in one's nature was to be approved as tending to the development of life. Could this assertion be made, there might be no difficulty in ethics, or rather, there might be no ethics at all, because there would be no difficulty in conduct. It is obvious, however, that the development of one natural tendency often conflicts with that of another in the same individual, as well as with the tendencies of other individuals. The course of evolution has no doubt tended to modify, though it has not rooted out, the impulses which are most prejudicial to individual and social welfare. But the increase of wants as well as satisfactions which it has brought about in human nature, makes it doubtful whether it has on the whole tended to diminish the conflict of motives. [Sidenote: implies distinction between permanent and transient self;] Again, when it is said that a man should "be himself," or that this is his "strongest tendency,"[251] there is an implicit reference to a distinction between a permanent and a transient, or a better and a worse self, and it seems to be imagined that this distinction can be reduced to difference in degrees of strength. But evolution has not enabled us to obviate Butler's objection to taking the "strongest tendency"--meaning by this the tendency which is at any time strongest--as representing "nature." For it is an undeniable fact that the tendency which for a time is the strongest--it may even be that which is strongest throughout an individual life--frequently leads to a diminution of vital power on the part of the agent, as well as to interference with the free exercise of the vital powers of others. Some advantage is gained, perhaps, by substituting for "strongest" the nearly equivalent phrase "most persistent" tendency. All those impulses which have in the past served to promote life have been chosen out and stored up as a sort of permanent basis for the human fabric; whereas other impulses, not so advantageous in their effects, have a less permanent influence, though they are not less real. The more regular or persistent class of impulses may, therefore, (the idea is) be taken as representing the course of the evolution by which they have been produced. [Sidenote: but includes non-moral impulses in the former,]