Mother (noun): 1 a female parent; 2 one's female parent; 3 a mother-in-law, step mother, or adoptive mother; 4. A woman exercising control, influence, or authority like that of a mother.
All of those words are true but somehow miss the fuller definition. A mother is the bearer of life, the nurturer of that life, the hub of the family and/or household, and in many cases the authority to whom one answers. The old saying, "mother rules the roost," has a lot of truth to it.
Starting with Freud, the mother seemed to become either the saint who made the children what they are or the devil who made them what they are. Since many film makers are self analytical types, it's not surprising that the movie mother has also ended up being either angel or demon. Oddly enough, the mother is often portrayed as an angel in films concerning boys and young men and as a devil with daughters (though there are exceptions, to be sure).
