and the demands, insusceptible of fulfillment, made against it. Let me
emphasize in the first place that whatever is here presented is derived
entirely from every-day medical experience which is to be made more
profound and scientifically important through the results of
psychoanalytic investigation. The "Three Contributions to the Theory of
Sex" can contain nothing except what psychoanalysis obliges them to
accept or what it succeeds in corroborating. It is therefore excluded
that they should ever be developed into a "theory of sex," and it is
also quite intelligible that they will assume no attitude at all towards
some important problems of the sexual life. This should not however give
the impression that these omitted chapters of the great theme were
unfamiliar to the author, or that they were neglected by him as
something of secondary importance.

The dependence of this work on the psychoanalytic experiences which have
determined the writing of it, shows itself not only in the selection but
also in the arrangement of the material. A certain succession of stages
was observed, the occasional factors are rendered prominent, the
constitutional ones are left in the background, and the ontogenetic
development receives greater consideration than the phylogenetic. For
the occasional factors play the principal rôle in analysis, and are
almost completely worked up in it, while the constitutional factors only
become evident from behind as elements which have been made functional
through experience, and a discussion of these would lead far beyond the
working sphere of psychoanalysis.

A similar connection determines the relation between ontogenesis and
phylogenesis. Ontogenesis may be considered as a repetition of
phylogenesis insofar as the latter has not been varied by a more recent
experience. The phylogenetic disposition makes itself visible behind the