How do we know that some beings have a status as 'persons' and some beings do not? If we attempt to delineate certain characteristics of personhood, we run into the quandary of, say, labelling the mentally ill as non-persons or labelling cancer cells as persons. Is this a problem? Is there a way to avoid this? Must we have the rights which personhood entails in the first place?

A person (from the Latin persona, mask) is merely one who has standing as a legal agent, and so, almost without exception, a person is a human being. (There is a body of law in the United States which suggests that groups of persons, in particular corporations, are also sometimes to be taken as persons, but this extension is best understood as a so-called legal fiction.) The mentally ill are persons because they are human beings. Cancer cells are not, for they are not human beings and they have no legal standing. There is not much more philosophical difficulty, as I see it, about the concept human being than there is about the concept squirrel , a member of the family Sciuridae, flat-tailed creatures, as a human being is simply a member of the species H. sapiens, a species that has "sapiens", wisdom or understanding, uses tools, and has language. The important thing is that we define the species, and then ask whether this specimen of whatever (the mentally ill person, the cancer cell) belongs to the species. I'm also not seeing which characteristics of mentally ill persons you think might threaten to make them non-persons, and which characteristics of cancer cells you think might suggest that cancer cells could be taken as persons.

Read another response by Jonathan Westphal
Read another response about Ethics