<p>It's not. You can create your own interdisciplinary concentration, but I think only about 1-2 students a year do that (often in bioethics). Otherwise you concentrate (major) in one subject and get one or more certificates (minors) in others. The certificate (minor) is really the equivalent of the concentration, or very close to that, in terms of the number of courses you take. The difference is that with the certificate you are not doing all the independent work.</p>