Westermarck would regard the objection to intercourse between those living together from youth as due to the biological causes discussed above (3). Without denying the truth of this view, we may venture to suggest that there perhaps exist psychological causes, which tend to bring about the same result. Those who live much together must necessarily react in and to each other's presence in a great variety of ways, involving a very considerable number of instinctive and habitual mechanisms, the majority of which are not--or at most are only quite indirectly--sexual in nature, being concerned for the most part with life preserving activities (_e. g._ obtaining and preparing food, eating, washing, dressing, acquiring or practising various branches of skill or knowledge, the carrying on of professional activities, _etc._). During the greater part of their time together, the sexual instincts of the persons concerned are therefore held in check in order that the other mental trends involved in these various necessary functions may enjoy full play; in fact the reaction to each other's presence along the lines of these other trends becomes much more habitual than does reaction along the lines of sexual feeling. The very constant inhibition of this latter feeling occasioned by the almost continual preoccupation with everyday affairs, in which those who live together are equally concerned, is apt to make it difficult for the inhibition to be entirely removed and for the sexual trends to have free play, even when opportunity offers; and is therefore calculated to make a union between those whose lives have long been intimately connected appear unsuitable or unattractive, quite apart from the operation of any definite taboo or prohibition; whereas with strangers inhibitions of the kind just described are far less operative and the sexual impulses can therefore work without impediment. [Sidenote: and especially by hostile tendencies] A further factor which may reinforce the foregoing is connected with the actual hostility (conscious or repressed) that so frequently exists between those whose lives and interests are connected. As we have already had occasion to see, the competition that exists between members of the same family is almost bound to engender some degree of hostility; and this hostility (even if in later life it be quite indiscernible to consciousness) will add its weight to any force which tends to inhibit love of the person towards whom hostility is felt. Here then we have two factors, which, though not peculiar to incestuous relationships, nevertheless very probably contribute a certain share of influence to the sum total of the forces productive of the aversion to incest[263]. [Sidenote: The incest tendencies are also affected by the general sexual inhibitions]