1. The conflict between the mother and the husband for the possession of the daughter and her belongings. The mother having in the majority of cases in the past enjoyed a greater or less degree of authority over the daughter, is loth to abandon this source of power, and seeks to retain it by exercising (through the frequent giving of advice, appeal to her own greater experience or otherwise) some sort of control over the daughter's household or mode of life. This interference on the part of the mother-in-law in the domestic arrangements of the younger couple is very apt to be resented by the son-in-law, either directly, because it appears to threaten his own supreme control over his own family, or indirectly, because he identifies himself with the daughter (his wife) who in her turn may not unnaturally object to the continuance of maternal supervision after her marriage. On the other hand, should the daughter display a marked tendency to be influenced by her mother or a high degree of veneration or affection for her, the son-in-law will again resent the interference of the latter, as threatening an encroachment on his wife's love and respect towards himself.
2. The husband's fear of losing (through too intimate contact with his mother-in-law) the sense of sexual attractiveness which his wife possesses for him. The mother-in-law reminds him of his wife, but is without her youthful beauty and this is apt to produce in him a dim sense of apprehension lest, as a result of seeing, as it were, the mother in the daughter, and of vaguely realising that the daughter may one day come to resemble the mother, the former may lose for him her charm and his whole marriage become thereby distasteful.
Of these two motives tending to produce disagreement between mother-in-law and son-in-law, the first is for the most part situated at or near the surface of consciousness, while the second can in many cases be brought to consciousness by the exercise of a little courageous introspection. Both motives, however (especially the second), are liable to be reinforced by two further motives, which remain for the most part buried in the Unconscious.
3. The mother-in-law may re-awaken in the son-in-law, in the manner we have already indicated, feelings which are incestuous in origin, being a displacement of those originally directed towards his own mother; the repression of these feelings of affection then giving place to their opposite--a feeling of repulsion or hostility--as a means of preventing the irruption into consciousness of the tabooed incestuous desires. As some indication of the reality of this factor, apart from the results of psycho-analysis, may be mentioned the fairly well recognised facts that it is possible for a man to be attracted to his future mother-in-law before he falls in love with his future wife, that he may hesitate as to whether he shall marry mother or daughter, or that he may fall back upon the mother should the daughter die or fail him in some other way. As further evidence too--on the negative side--we may refer to the extraordinarily numerous and widespread taboos and "avoidances" which affect the relations between son-in-law and mother-in-law among primitive peoples.