http://www.ccel.org/ccel/aquinas/summa.FP_Q92_A1.html
Reply to Objection 1: As regards the individual nature, woman is defective and misbegotten, for the active force in the male seed tends to the production of a perfect likeness in the masculine sex; while the production of woman comes from defect in the active force or from some material indisposition, or even from some external influence; such as that of a south wind, which is moist, as the Philosopher observes (De Gener. Animal. iv, 2). On the other hand, as regards human nature in general, woman is not misbegotten, but is included in nature's intention as directed to the work of generation. Now the general intention of nature depends on God, Who is the universal Author of nature. Therefore, in producing nature, God formed not only the male but also the female.
Reply to Objection 2: Subjection is twofold. One is servile, by virtue of which a superior makes use of a subject for his own benefit; and this kind of subjection began after sin. There is another kind of subjection which is called economic or civil, whereby the superior makes use of his subjects for their own benefit and good; and this kind of subjection existed even before sin. For good order would have been wanting in the human family if some were not governed by others wiser than themselves. So by such a kind of subjection woman is naturally subject to man, because in man the discretion of reason predominates. Nor is inequality among men excluded by the state of innocence, as we shall prove (Q[96], A[3]).
Reply to Objection 1: As regards the individual nature, woman is defective and misbegotten, for the active force in the male seed tends to the production of a perfect likeness in the masculine sex; while the production of woman comes from defect in the active force or from some material indisposition, or even from some external influence; such as that of a south wind, which is moist, as the Philosopher observes (De Gener. Animal. iv, 2). On the other hand, as regards human nature in general, woman is not misbegotten, but is included in nature's intention as directed to the work of generation. Now the general intention of nature depends on God, Who is the universal Author of nature. Therefore, in producing nature, God formed not only the male but also the female.
Reply to Objection 2: Subjection is twofold. One is servile, by virtue of which a superior makes use of a subject for his own benefit; and this kind of subjection began after sin. There is another kind of subjection which is called economic or civil, whereby the superior makes use of his subjects for their own benefit and good; and this kind of subjection existed even before sin. For good order would have been wanting in the human family if some were not governed by others wiser than themselves. So by such a kind of subjection woman is naturally subject to man, because in man the discretion of reason predominates. Nor is inequality among men excluded by the state of innocence, as we shall prove (Q[96], A[3]).