For example, questions about the morality of abortion often pivot on the following question: is a foetus a person or not? A person is, roughly, someone who has similar moral status to a normal adult human being. Being a person is not simply the same thing as being a member of the human species, however, since it is at least possible that some human beings are not persons (brain-dead individuals in permanent comas, for example?) and some persons might not be human beings (intelligent life from other planets, or gorillas, perhaps?). If it turns out that a foetus is a person, abortion will be morally problematic—it may even be a kind of murder. On the other hand, if a foetus is no more a person than, say, one of my kidneys, abortion may be as morally permissible as a transplant. So is a foetus a person? How would one even go about discovering the answer to this question? Philosophers proceed by using conceptual analysis. What we need to find out, first of all, is what makes something a person—what the essential difference is between persons and non-persons—and then we can apply this general account to human foetuses to see if they satisfy the definition. Put another way, we need to discover precisely what the word person means.

Since different conceptual analyses will provide importantly different answers to questions about the morality of abortion, we need to justify our definition: we need to give reasons to believe that one particular analysis of personhood is correct. This is where logic comes in: logic is the study of arguments, and its techniques are designed to distinguish between good arguments—by which we should be persuaded—and bad arguments, which we should not find persuasive.


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