  The main aim of this paper is to present the ideas which lead first to the
solution of the unitarizability problem for $\GL(n)$ over nonarchimedean local
fields and to the recognition that the same result holds over archimedean local
fields, a result which was proved by Vogan using an internal approach. Let us
say that the approach that we are going to present may be characterized as
external. At no point do we go into the internal structure of representations.
