The extension of feminism (understood as a practical social movement concerned to address the inequality of the sexes) into theoretical discourse. Undoubtedly one of the most important and influential intellectual currents of the 20th century (every bit the equal of Marxism and psychoanalysis), Feminist theory encompasses most disciplines from art and architecture through to science and technology, but it is predominantly concentrated in the social sciences and the humanities. As diverse as it is, and the varieties of feminist theory are almost without limit, at its core it has four principal concerns, which are to: (i) elucidate the origins and causes of gender inequality; (ii) explain the operation and persistence of this state of affairs; (iii) delineate effective strategies to either bring about full equality between the sexes or at least ameliorate the effects of ongoing inequality; and (iv) imagine a world in which sexual inequality no longer exists. Of the four, feminist theory has tended to prioritize the first two, leaving the strategic questions to women working in the field, so to speak, in the various advocacy groups like the National Organization for Women founded in the US in 1966; while the task of imagining the future has been parcelled out to creative writers, particularly those working in SF like Ursula LeGuin and Marge Piercy. The decision to prioritize one or other of these four problematics is what gives shape to the specific feminisms.
The causes of sexual inequality are almost impossible to trace since for all of recorded history it was already an established fact. Therefore it is ultimately a matter for pure speculation. The most widely accepted hypothesis is that in prehistoric times biology placed women in a subordinate position to men because pregnancy and childrearing render them vulnerable and in need of assistance both to obtain food and fend off predators. While there is probably some truth to this strand of the biological determinism hypothesis from an anthropological point of view, the practical need to protect women does not explain the widespread denigration of women and their socialization as lesser beings. By the same token, as societies became more prosperous and their technology more sophisticated women's vulnerability diminished, but if anything the positioning of them assubordinate seemed to harden. For obvious reasons, then, the issue that has exercised feminist theorists the most is the one of persistence: why does sexism continue after the principal justification for it has long since ceased to obtain?
There are three basic answers to this question: first, biology continues to be a determining factor; second, that it is in men's interest to maintain the subordination of women; and third, women have been complicit with their own oppression. Surprisingly, perhaps, radical feminists like Shulamith Firestone support the first answer, although she then uses it as a stage to call for the use of biotechnology to put an end to women's reproductive role. Not surprisingly, the second answer has very widespread support, and shows the influence of Marxism. In effect, it equates feminist struggle with class struggle. The third answer, which is perhaps the most painful inasmuch as it is a form of self-criticism, has given rise to the most debate, and perhaps for that reason has contributed the most in the way of ideas for achieving the strategic goal of equality between the sexes. Both First Wave and Second Wave feminists agree that femininity—understood as a male-imposed ideal of how women should look and act—is a major limiting factor for feminist politics. So from Mary Wollstonecraft to Germaine Greer and Kate Millett feminist writers have advocated to a greater or lesser degree the abandoning of the practice of self-denial most versions of femininity demand. Interestingly, some Third Wave feminists have argued against this, calling instead for a celebration of femininity.