In ethical theory one deals with questions about what is good or rational to do by referring to practical reasons.Bernard Williams's Internalism is such a theory of practical reasons. His main claim is that practical reasons are conditionally normative -they must rest on a psychological foundation. If we say of someone that they have reason to do something, we can only do that if the person himself could, by some sort of sound reasoning, concur with such a judgement. Externalism of practical reasons does not have such a requirement. What people have reasons to do is provided by truth independently of any person's psychological make up.
In this thesis I argue that internalism is right in forcing a psychological demand on ethical theories. In essence this means that ethical theory needs pedagogy, and that internalism is that which meets such a demand best. However, internalism might be basing itself on a wrong picture of psychology. McDowell accepts the psychological demand on ethical theories, but he offers a different account of psychology that is more congenial to the externalist interpretation of reasons.