The usefulness of a biological approach to ethics depends on what ethics is. If it is just a certain type of behavioral pattern or habit, accompanied by some emotional responses, then biological theories can be expected to teach us a great deal about it. But if it is a theoretical inquiry that can be approached by rational methods, and that has internal standards of justification and criticism, the attempt to understand it from outside by means of biology will be much less valuable. This is true for the same reason that the search for a biological explanation of mathematical or physical theories, or biological theories for that matter, would be relatively futile. First, we have no general biological understanding of human thought. Second, it is not a fixed set of behavioral and intellectual habits but a process of development that advances by constant reexamination of the total body of results to date. A being who is engaged in such an open-ended process of discovery cannot at the same time understand it fully from outside: otherwise he would have a decision procedure rather than a critical method. In most interesting subjects we do not want a decision procedure because we want to pursue a deeper level of understanding than that represented by our current questions and the methods we have for answering them.