What's often called 'second-wave' feminism is sometimes dated to begin with the publication of The Second Sex by Simone De Beauvoir in 1949. De Beauvoir herself was critical of that claim later in life; whilst acknowledging that she had some influence on the women's movement that grew in the 1960s, she argued that it had other more pressing, contemporary influences.
It's a long book. Over 700 pages. So why is it worth reading a book long on how women have been treated in philosophy and literature and short on the specifically political? The pre-WW1 British women's suffrage movement is glossed over in less then a page but the George Elliot novel The Mill on the Floss gets three or four pages, for instance.
The Second Sex is not some kind of bible of the women's movement. De Beauvoir herself in interviews in the 1970s admitted that her book had dated; that she was not addressing a live movement. Her engagement with the women's movement as an activist came later in life. But it's important because it brought to feminist thought a whole raft of ideas that still resonate today.
One of the two main theses of the book is that, through education and culture, women are seen in both male and female consciousness as the "the other". She talks about how in Christianity and other religions the male is seen as the ideal or default form and women's bodies, experience and role has been defined through perceived difference to men's: "Thus humanity is male and man defines woman not herself but as relative to him."
This sense of women as "the other" is all-pervasive within culture, literature, art and philosophy. It is why the French Revolution and Age of Enlightenment were able to proclaim universal human rights while not even considering if they applied to women.
The idea of "the other" and othering has been taken up by cultural studies, critical theory and elsewhere. However, De Beauvoir saw the condition and position of women in society throughout history as determining this category of "the other", not "the othering" determining the condition and position of women in society.
The other major thesis speaks right to the heart of debates in the women's movement today: how much is womanhood socially, ideologically and economically defined by biology? De Beauvoir never uses the word gender but makes a clear distinction between "woman" and biological sex.
In her chapter on childhood she famously says,
"one is not born, but rather one becomes, woman. No biological, psychic or economic destiny defines the figure that the human female takes on in society."
She doesn't entirely discount the role of biology or economic factors in historically driving women's oppression, or as an aspect of it today, but in her view, it is not the determinating factor. She says,
"the woman's body is one of the essential elements of the situation she occupies in this world. But her body is not enough to define her; it has a lived reality only as taken on by consciousness through actions and within a society; biology alone cannot provide an answer to the question that concerns us: why is woman the Other?"
She also believed that modern technology, women's changing role in work and scientific advances such as birth control, automation and modern medicine, have radically reduced women's potential "enslavement to the species" and made women's liberation possible in a far more radical way then it was in the past.
As for the role of the economic in women's oppression, De Beauvoir generally saw herself as deeply influenced by Marxism but not a Marxist, as such. In 1949 she was somewhat close to the Stalinist Communist Party, although she criticises the revival, under Stalin, of "patriarchal theories of marriage". She also makes a distinction between the USSR and 'democratic socialism'. She believed that being determines consciousness:
"woman's consciousness of herself is not defined by her sexuality alone: it reflects a situation that depends on society's economic structure."
But she is critical of Engels' account of women's oppression beginning with private property. She is critical of an economist or reductionist explanation of women's oppression. Women's consciousness is not just defined by her relationship to private property and class struggle. There exists a broader "existential architecture" of women's oppression that goes beyond and pre-dates the capitalist mode of production, or even private property.
There are contradictions in De Beauvoir's writing, she does not offer any real political answers, and can end up seeming to point towards women's consciousness as the be all and end all of struggle. However, her ideas are important for socialist feminists interested in the whole of women's experience and consciousness.