A foundational discipline would be a discipline such that fundamental issues resolved in it have direct and indirect bearing on issues in other disciplines. These latter issues are assumed to be (primarily) methodological and secondary (see methodology); the solution of the "fundamental issues" themselves is supposed to be independent of the resolution of issues in those other disciplines. That is, some matters in discipline B are to be isolated and dealt with using discipline A alone.

It is philosophically tendentious to say that there are any foundational disciplines: it perhaps betrays a very controversial view in philosophy, namely foundationalism. For purposes of classification, however, it can be useful to regard philosophy and mathematics and statistics -- at least -- as examples.