The forgetting of impressions and experiences shows the working of the tendency to ward off from memory that which is unpleasant much more clearly and invariably than the forgetting of names. It does not of course belong in its entirety to the category of errors, but only in so far as it appears to us remarkable and unjustified, judged by the standard of general experience; as, for instance, where recent or important impressions are forgotten, or where one memory is forgotten out of an otherwise well-remembered sequence. How and why we have the capacity of forgetting in general, particularly how we are able to forget experiences which have certainly left the deepest impression on us, such as the events of our childhood, is quite a different problem, in which the defence against painful associations plays a certain part but is far from explaining everything. That unwelcome impressions are easily forgotten is an indubitable fact. Various psychologists have remarked it; and the great Darwin was so well aware of it that he made a golden rule for himself of writing down with particular care observations which seemed unfavourable to his theory, having become convinced that just these would be inclined to slip out of recollection. Those who bear for the first time of this principle of defence against unpleasant memory by forgetfulness seldom fail to raise the objection that, on the contrary, in their experience it is just that which is painful which it is hard to forget, since it always comes back to mind to torture the person against his will—as, for example, the recollection of grievances or humiliations. This fact is quite correct, but the objection is not sound. It is important to begin early to reckon with the fact that the mind is an arena, a sort of tumbling-ground, for the struggles of antagonistic impulses; or, to express it in non-dynamic terms, that the mind is made up of contradictions and pairs of opposites. Evidence of one particular tendency does not in the least preclude its opposite; there is room for both of them. The material questions are: How do these opposites stand to one another and what effects proceed from one of them and what from the other?