In this article, I explore the accounts of marriage, concubinage, and prostitution given by Kant in his The Metaphysics of Morals and Lectures on Ethics and by Fichte in his Foundations of Natural Right. Both Kant's and Fichte's accounts of marriage have been analyzed from the feminist perspective, beginning with Marianne Weber's work in 1907. Many of these feminist analyses, however, have been so devoted to criticizing Fichte's views about marriage and gender that they have overlooked what his views about concubinage and prostitution entail when he argues for the concept of marriage. Similarly, Kant's views about marriage and gender have been the target of fierce criticisms by contemporary feminist thinkers. However, drawing on Kant's philosophy, some anti-prostitution feminist thinkers morally condemn prostitution. As a result, the problem of how Kant's and Fichte's discourses contribute to divisions among women has been disregarded. This paper aims to show how Kant and Fichte, regardless of their intention, discursively produce divisions among women. The argument of this paper proceeds as follows. First, to summarize Kant's views on sexual impulse, in Kant's words Geschlechtsneigung, and show how and why he criminalizes concubinage and prostitution, I analyze the discussion on the duty to oneself in his Lectures on Ethics in the mid-1770s (Section 1). Next, through a close reading of the “Casuistical Questions” in Part II of his Metaphysics of Morals, Tugendlehre, I show Kant's view about whether engaging in sex in marriage is permissive when a married couple can engage in sex without taking account of the possibility of procreation, that is, when they know that procreation is not possible (Section 2). Furthermore, I show how Fichte in his Foundations of Natural Right defines the natures of women and men and then deduces from his definition of sexes the necessity of marriage (Section 3). Finally, I demonstrate how Fichte defines concubinage and prostitution in his theory of marriage (Section 4). I conclude that in the Kantian framework engaging sex only for the sake of sexual pleasure, even in marriage, can be morally impermissible. I also argue that a woman's consent to her absolute and infinite subordination, which Fichte requires for a just marriage, cannot be based on her free will.