The categorical imperative incorporates two criteria for determining moral right and wrong: universalizability and reversibility. Universalizability means the person's reasons for acting must be reasons that everyone could act on at least in principle. Reversibility means the person's reasons for acting must be reasons that he or she would be willing to have all others use, even as a basis of how they treat him or her. That is, one's reasons for acting must be reasons that everyone could act upon in principle, and the person's reasons must be such that he would be willing to have all others use them as well. Unlike utilitarianism, which focuses on consequences, Kantian theory focuses on interior motivations. The second formulation Kant gives of the categorical imperative is this: "Act in such a way that you always treat humanity, whether in your own person or in the person of any other, never simply as a means, but always at the same time as an end." Or never treat people only as means, but always also as ends. What Kant means by "treating humanity as an end" is that everyone should treat each human being as a being whose existence as a free rational person should be promoted. For Kant, this means two things: (a) respect each person's freedom by treating people only as they have freely consented to be treated beforehand, and (b) develop each person's capacity to freely choose for him or herself the aims he or she will pursue. Kant's second version of the categorical imperative can be expressed in the following principle: "An action is morally right for a person if, and only if, in performing the action, the person does not use others merely as a means for advancing his or her own interests, but also both respects and develops their capacity to choose freely for themselves." This version of the categorical imperative implies that human beings have an equal dignity that sets them apart from things such as tools or machines and that is incompatible with their being manipulated, deceived, or otherwise unwillingly exploited to satisfy the self-interests of another.
However, even if the categorical imperative explains why people have moral rights, it cannot by itself tell us what particular moral rights humans have. And when rights come into conflict, it cannot tell us which right should take precedence. Still, there seem to be three basic rights that can be defended on Kantian grounds:
1. Humans have a clear interest in being provided with the work, food, clothing, housing, and medical care they need to live.
2. Humans have a clear interest in being free from injury and in being free to live and think as they choose.
3. Humans have a clear interest in preserving the institution of contracts. Despite the attractiveness of Kant's theory, critics have argued that, like utilitarianism, it has its limitations and inadequacies. A first problem that critics have traditionally pointed out is that Kant's theory is not precise enough to always be useful. Second, some critics claim that although we might be able to agree on the kinds of interests that have the status of moral rights, there is substantial disagreement concerning what the limits of each of these rights are and concerning how each of these rights should be balanced against other conflicting rights. A third group of criticisms that have been made of Kant's theory is that there are counterexamples that show the theory sometimes goes wrong. Most counterexamples to Kant's theory focus on the criteria of universalizability and reversibility.
A very different view of rights is based on the work of libertarian philosophers such as Robert Nozick. They claim that freedom from constraint is necessarily good, and that all constraints imposed on one by others are necessary evils, except when they prevent even greater human constraints. The only basic right we all possess is the negative right to be free from the coercion of other...