In philosophy, the matter of personal identity deals with such questions as, "What makes it true that a person at one time the same thing as a person at another time?" or "What kinds of things are we persons?" The term "identity" in "personal identity" refers to "numerical identity," where saying that X and Y are numerically identical just means that X and Y are the same thing. Personal identity is not the same as personality, though some theories of personal identity maintain that continuity of personality may be required for one to persist through time. In relation to answer questions about persistence, such as under what conditions a person does or does not continue to exist, contemporary philosophers often seek to first answer questions about what sort of things we are, most fundamentally. Many people claim we are animals, or organisms, but many others strongly believe that no person can exist without mental traits, such as consciousness. Since an organism can exist without consciousness, both these views cannot be true (if we are organisms we can exist without being conscious; but if we can't exist without consciousness, we are not organisms). Thus, in order to determine whether certain features (such as consciousness) are crucial to a person's continued existence, it may be important to first ask what sort of things we are.