Philosophical literature offers different answers to the question of which qualities a living creature must have in order to be a bearer of rights (moral patient). Depending on the particular approach adopted, certain species of animal fall within the group of potential moral patients. The following section adumbrates a number of approaches.

(A) Philosophers such as Joel Feinberg and Leonard Nelson argue that all living creatures which have the capacity for feeling and hence have an interest in a pain-free existence are also entitled to a corresponding right (to freedom from pain).

(B) As a refinement of approach A, other authors (for example Raymond Frey) suggest that only creatures with more extensive cognitive abilities such as the capacity for language (instead of purely the capacity to feel) would have interests (preferences). In this understanding man is the only living creature that has interests and hence can be a bearer of rights.

(C) The status of moral patient can also be substantiated by the capacity for moral action (as expressed for example by Immanuel Kant or by Friedo Ricken in relation to Kant). Accordingly, the only living creatures that can be bearers of rights are those that can also be bearers of obligations to other living creatures. The category of "moral patients" would thus be identical to that of "moral agents".

If - as in the aforementioned approaches - the status of moral patient is established by the existence of certain qualities (capacity to feel, capacity for language, capacity for moral action), some human beings will also initially be excluded from the category of bearers of rights. Yet most theories take the view that all humans, irrespective of their qualities and capacities, are bearers of rights. Two modes of argumentation may be presented that resolve this dilemma.

(1) On the one hand, it may be argued that not only the present but also the potential qualities of a living creature determine its status as a moral patient. Infants, for example, do not have the qualities required for the status of moral patient, but they will acquire them in the course of their life. If the predisposition towards a capacity for language or a capacity for moral action were to suffice for the bearing of rights, infants (but not animals of "equal capacity") would have rights, even though they do not yet have the required qualities.

(2) On the other hand, it may be argued that the bearing of rights does not derive from individual present or potential qualities, but from qualities that are typical of the species. A severely mentally handicapped person or a coma patient who did not meet the aforementioned criteria for the status of moral patient would therefore be a moral patient because he or she belonged to a species that typically had the required qualities.