The aim of this paper is to give an approach to Shelah's classification theory. The author has the sure hope that the ideas of classification theory will find good applications beyond the confines of model theory. So he discusses them in the form of pictures, sometimes rather vague, of how things ought to be. The paper is built around eleven ideas. The most useful notions are those of dimension and good complete first order class, i.e. such a complete class that every structure in it can be specified up to isomorphism by dimensional invariants of the fixed kind. The author concentrates on these notions and a few ideas connected with them. There are illustrative examples in the paper, too.