Some of you have asked offline: "Where's the definitive proof Aristotle was sexist?"
The two best contemporary works I've read that answer this question are the following:
Feminism In Greek Literature From Homer To Aristotle (first published in 1923) by F. A. Wright
The Concept of Woman: The Aristotelian Revolution 750 Bc-Ad 1250 (1997) by Prudence Allen
Allen thoroughly reviews everything extant that Aristotle ever wrote or said (or was quoted as writing or saying) about women. She carefully identifies how Aristotle's statements on woman relate to four categories important to his predecessors: Opposites, Generation, Wisdom, and Virtue. Then Allen summarizes for us, and comments on, what Aristotle has said:
1. The male is separated from the female, since it is something better and more divine in that it is the principle of movement for generated things, while the female serves as their matter.
2. A woman is as it were an infertile male.
3. The female is as it were a deformed male.
4. The male is by nature superior, and the female inferior; and the one rules, and the other is ruled.
In these statements the superior valuation of man over woman is explicitly stated. However, it is also present in the theory of contraries and in other aspects of Aristotle’s thought about sex identity. Aristotle stands out from his predecessors in that he gave a complete rationale for his theory of sex polarity. He developed reasons and arguments for the philosophically significant differentiation of the sexes and for the superiority of man over woman. Therefore, he is correctly identified as the founder of the sex polarity position. . . . [H]e also laid the groundwork for another theory of sex identity in his philosophy of definition. (page 121)
Wright gives direct quotes of all the salient texts of Aristotle on "women." Then he ends his book by saying:
. . . In every department of civilized existence the influence of Aristotle must still be taken into account, and his judgment of women's positions in society--a view sincerely held and on the whole most temperately expressed--has had far more effect on the world than have the idealist theories of Plato. . . . In Aristotle's time, for reasons which this brief survey of Greek literature has, perhaps, made plain, the facts of women's nature were certainly not sufficiently comprehended. . . [A]ny true appreciation of a woman's real qualities, . . . Aristotle, by the whole trend of his prejudices, was opposed. His mistake was that he failed to realise the moral aspects of feminism. A nation that degrades its women will inevitably suffer degradation itself. Aristotle lent the weight of his name to a profound error, and helped to perpetuate the malady which had already been the chief cause of the destruction of Greece. (pages 202, 222)
[update: other works by others are here.]