Kant believed that the shared ability of humans to reason should be the basis of morality, and that it is the ability to reason that makes humans morally significant. He therefore believed that all humans should have the right to common dignity and respect. Margaret Eaton argues that, according to Kant’s ethics, a medical professional must be happy for their own practices to be used by and on anyone, even if they were the patient themselves. For example, a researcher who wished to perform tests on patients without their knowledge must be happy for all researchers to do so. She also argues that Kant’s requirement of autonomy would mean that a patient must be able to make a fully informed decision about treatment, making it immoral to perform tests on unknowing patients. Medical research should be motivated out of respect for the patient, so they must be informed of all facts, even if this would be likely to dissuade the patient. Jeremy Sugarman has argued that Kant’s formulation of autonomy requires that patients are never used merely for the benefit of society, but are always treated as rational people with their own goals. Aaron Hinkley notes that a Kantian account of autonomy requires respect for choices that are arrived at rationally, not for choices which are arrived at by idiosyncratic or non-rational means. He argues that there may be some difference between what a purely rational agent would choose and what a patient actually chooses, the difference being the result of non-rational idiosyncrasies. Although a Kantian physician ought not to lie to or coerce a patient, Hinkley suggests that some form of paternalism – such as through withholding information which may prompt a non-rational response – could be acceptable.
In her work How Kantian Ethics Should Treat Pregnancy and Abortion, Susan Feldman argues that abortion should be defended according to Kantian ethics. She proposed that a woman should be treated as a dignified autonomous person, with control over their body, as Kant suggested. She believes that the free choice of women would be paramount in Kantian ethics, requiring abortion to be the mother’s decision. Dean Harris has noted that, if Kantian ethics is to be used in the discussion of abortion, it must be decided whether a fetus is an autonomous person. Kantian ethicist Carl Cohen argues that the potential to be rational or participation in a generally rational species is the relevant distinction between humans and inanimate objects or irrational animals. Cohen believes that even when humans are not rational because of age (such as babies or fetuses) or mental disability, agents are still morally obligated to treat them as an ends in themselves, equivalent to a rational adult such as a mother seeking an abortion.
Kant viewed humans as being subject to the animalistic desires of self-preservation, species-preservation, and the preservation of enjoyment. He argued that humans have a duty to avoid maxims that harm or degrade themselves, including suicide, sexual degradation, and drunkenness. This led Kant to regard sexual intercourse as degrading because it reduces humans to an object of pleasure. He admitted sex only within marriage, which he regarded as “a merely animal union”. He believed that masturbation is worse than suicide, reducing a person’s status to below that of an animal; he argued that rape should be punished with castration and that bestiality requires expulsion from society. Feminist philosopher Catharine MacKinnon has argued that many contemporary practices would be deemed immoral by Kant’s standards because they dehumanise women. Sexual harassment, prostitution and pornography, she argues, objectify women and do not meet Kant’s standard of human autonomy. Commercial sex has been criticised for turning both parties into objects (and thus using them as a means to an end); mutual consent is problematic because in consenting, people choose to objectify themselves. Alan Soble has noted that more liberal Kantian ethicists believe that, depending on other contextual factors, the consent of women can vindicate their participation in pornography and prostitution.
Because Kant viewed rationality as the basis for being a moral patient—one due moral consideration—he believed that animals have no moral rights. Animals, according to Kant, are not rational, thus one cannot behave immorally towards them. Although he did not believe we have any duties towards animals, Kant did believe being cruel to them was wrong because our behaviour might influence our attitudes towards human beings: if we become accustomed to harming animals, then we are more likely to see harming humans as acceptable.
Ethicist Tom Regan rejects Kant’s assessment of the moral worth of animals on three main points: First, he rejects Kant’s claim that animals are not self-conscious. He then challenges Kant’s claim that animals have no intrinsic moral worth because they cannot make moral judgement. Regan argues that, if a being’s moral worth is determined by its ability to make a moral judgement, then we must regard humans who are incapable of moral thought as being equally undue moral consideration. Regan finally argues that Kant’s assertion that animals exist merely as a means to an ends is unsupported; the fact that animals have a life that can go well or badly suggests that, like humans, they have their own ends.
Kant believed that the Categorical Imperative provides us with the maxim that we ought not to lie in any circumstances, even if we are trying to bring about good consequences, such as lying to a murderer to prevent them from finding their intended victim. Kant argued that, because we cannot fully know what the consequences of any action will be, the result might be unexpectedly harmful. Therefore, we ought to act to avoid the known wrong—lying—rather than to avoid a potential wrong. If there are harmful consequences, we are blameless because we acted according to our duty. Driver argues that this might not be a problem if we choose to formulate our maxims differently: the maxim ‘I will lie to save an innocent life’ can be universalised. However, this new maxim may still treat the murderer as a means to an end, which we have a duty to avoid doing. Thus we may still be required to tell the truth to the murderer in Kant’s example.