natural plan for human beings is inherently wrong. This teaching stipulates procreation as the natural purpose of sexuality, and thus sexual activity not open to the transmission of life is prohibited. In Humanae vitae, the most recent Catholic encyclical on the topic of sexuality, permanent monogamous marriage is stated as the only appropriate context for the fulfillment of moral sexuality. In this encyclical, both the unitive and procreative dimensions of sex must be present for a sexual encounter or sex act to be considered morally permissible. St. Thomas Aquinas and St. Augustine were some of the key figures in honing Christian ethics. Augustine underlined fidelity, offspring, and sacrament as the goods of sexual morality. Thomas Aquinas developed Augustine's thought to suggest that these ought to be understood as the three ends (telos) of marriage, and ranked them in order of importance, with procreation as the primary end. Philosophy Not until contemporary times has sex thought of as something generally good in the history of western philosophy: "Plato denigrated it, arguing that it should lead to something higher or better (Phaedrus, Symposium), Aristotle barely mentioned it, and Christian philosophers condemned it." A major topic in the philosophy of sex and related to the question of the moral status of sex is objectification, where sexual objectification is treating a person only as a sex object. The concept originates in Kant's moral philosophy, and many modern thinkers have used it to criticize and analyze a wide range of ethical issues related to sex, such as pornography. Kant views sex as only morally permissible in the context of a heterosexual, lifelong, and monogamous marriage, whereas any sexual act that is performed outside this context is considered morally wrong. This is due to Kant's interpretation of the Categorical Imperative with regard to sexual desire. He considers sex the only inclination that cannot satisfy the Categorical Imperative; in fact, sexual desire by its nature is objectifying and lends itself to the thing-like treatment of other persons. The solution to the overall problem of objectification and sex, on Kant's view, is marriage: Only marriage can make objectification tolerable. Kant argues that in a marriage, which is "a relationship that is structured institutionally in ways that promote and, at least legally if not morally, guarantee mutual respect and regard", objectification may be rendered harmless. Furthermore, not all sexual activity is necessarily objectifying here: sexual activity that does not