The natural tendency of all sexual thought and emotion is to find its outlet in physical expression of some kind. If a man indulges in sexual thought, it is almost impossible for him to avoid a physical result. He may have recourse to prostitution or he may commit solitary practices. The tendency of Puritan morality is, as we have seen, to regard the physical act as the sin and to avoid the conclusion that the thought is evil; consequently the patient is urged at all cost to refrain from action. Let it be stated, quite frankly, that this attitude is scientifically and morally indefensible. It is the thought rather than the act on which the responsibility should be weighed. I have no hesitation whatever in asserting that it is worse, medically and morally, for the individual to indulge in sexual thought and repress the consequent action, than to commit it. The mere absence of physical conduct is harmful and deplorable if the mind is a seething mass of sexual energy which is being denied all outlet. The first duty in such cases is, as we have seen, to apply the process of transmuting this sexual thought to non-sexual interests, so far as this can be done. The extent to which this is possible must vary in each individual nature. The comparative balance then remains. And here we must bring into play the moral principle to which I have already referred--namely that the morality of sex is determined by the extent to which love is the motive. Sex inspired by love is moral; sex inspired by any other motive is not. The part which the physical sex-force should alone play is the sacramental expression of pure love; so employed it is a perfect and divine activity. When the love-motive is absent, or is not the dominant incentive, the sex-force becomes comparatively immoral and abused. This is a general principle which can be rigidly employed. And I do not want to escape from the consequences of this doctrine. It appears to me the one natural, fundamental principle upon which a moral standard can be based. Therefore I am ready to accept the conclusion that there are many marriages which are highly immoral because the sex-act is not an expression of love, but either a mere mechanical duty or the result of a physical and emotional excitement, as distinct from love. On the other hand there are many sex adventures, inspired by love, which do not occur within the matrimonial state. This principle alone must guide us in any moral estimate we draw.