康德在性和婚姻問題上的態度是學者們最不願意為其辯護的話題。康德將人類的性欲視為動物性的本能衝動，並主張任何形式的性行為都將損害主體的人格尊嚴。婚姻是人類性行為的唯一合法形式。康德的這一主張甚至引起了很多開明人士的反感。事實上，這種消極保守的立場一方面植根於其所處的時代文化背景，另一方面也基於康德哲學強調理性至上的根本原則。儘管如此，作為啟蒙運動的代表，康德還是在很大程度上突破了其時代的局限性，在該問題上表現出積極樂觀的啟蒙思想。透過那種表面上消極保守的觀點，我們會發現，在康德哲學中，人類的性欲表現出更多道德性和文明性的色彩，在人類社會發展過程中扮演著重要的角色；婚姻的意義真正說來在於引導性欲朝著道德化和文明化的方向發展，婚姻是一個道德的共同體，旨在塑造更加完美的道德人。

Kant's attitude on sex and marriage is the last point which scholars will to justify. He regards sexual desire as the instinctive impulse of animals, and put forwards that any sexual behaviors must destroy the individual's personal dignity. Marriage is the only legal form for sexual activity. These arguments arouse dislikes by many enlightened person. In fact, such a negative standpoint is deeply resulted from the culture of western society at that time, as well as Kant's own principle about the superiority of reason. However, as the representative of Enlightenment, Kant breaks through the limitation of his era, and shows some positive enlightened thoughts. Beyond the negative arguments on the surface, we can find that, in Kant's philosophy, human sexual desire implies much more meaning of morality and civility, and plays an important role in the history of humankind. The real meaning for marriage is to make sexual desire develop towards morality and civilization. Marriage is a moral community, with the purpose to make men much more perfect and moralized.