Many have argued that a fundamental difference exists between the sexes; others deny this, saying that society to blame for teaching us our roles.

Jung was perplexed by this question, and his journey to find the answer took him into many different territories. He looked towards mythology, Eastern philosophies, various religions and even the occult for enlightenment. He educated himself in the work that was being done on the subject by others in the medical profession; he even consulted doctors whom were researching the roles of hormones. He read works by European mystics and philosophers, and he saw that alchemy had a lot to offer, as well as some of the more conventional sciences like archaeology and anthropology.

What Jung eventually hypothesised was the existence of a polarity within both sexes. He was inclined to believe that the matter of the distinction between the sexes could not be answered in a black-and-white manner. That is to say that rather than make the assertion that there is no real difference between the sexes, or that there is an undoubtable one, Jung claimed that we are all masculine and feminine by degrees.

Even medical science tells us that males have a minority of female hormones, while females have a minority of male hormones. Jung took the basics of this principle and applied it to Analytical Psychology, backing up his results with much empirical evidence.

 He pointed out that we all have a counterposition within us, a balance to our dominant sex. He stressed that this interplay between masculinity and femininity is not only a real phenomenon, but is perhaps the most important factor in our lives - and it was perhaps in this area that Carl Jung's greatest contribution lay.

He termed the feminine soul, or unconscious femininity, within a man the Anima; the masculine soul, or unconscious masculinity, within a woman he named the Animus. He took these from the Latin animare - to enliven - as he saw these as pushing us to a newer life.

Thus a man, his ego masculine, receives impulses from his Anima to recognise his inner femininity; a woman, her ego feminine, feels the pressure from her Animus to utilise her inner masculinity.

This theory was a major breakthrough, though simple in form compared to today. Jung himself said that men and women probably have both Anima and Animus within them; like much of his work, he willingly left this open for others to ponder while he forged ahead into no man's land.

Most people today who encounter Jung for the first time are invariably drawn to his psychology by the notion of contrasexuality in its simplistic form. Even today's Jungian psychologists introduce this theory to the uninitiated in basic terms. To talk immediately of the simultaneous existence of both forces only confuses the issue; one has first to understand what it means to have a living opposite to one's dominant sexuality.