We have been forced to perceive in every fixed aberration from the normal sexual life, a fragment of inhibited development and infantilism .... The perversions thus prove themselves to be, on the one hand, inhibitions, and on the other, dissociations from the normal development.
The union of the genitals in the characteristic act of copulation is taken as the normal sexual aim .... Yet, even in the most normal sexual act, certain addenda are distinguishable, the development of which may lead to aberrations described as perversions .... The perversions represent either (a) anatomical transgressions of the bodily regions destined for sexual union, or (b) a lingering at the intermediary relations to the sexual object which should normally be rapidly passed, on the way to the definite sexual aim.
Sadism and Masochism as Perversions
We use the word "sadism" when sexual satisfaction depends upon the sexual object suffering pain, ill-treatment and humiliation, and the word "masochism," when the subject himself has to suffer such treatment. You know, too, that there is a certain admixture of these two tendencies in normal sexual relations, and that we call them "perversions" when they thrust the other sexual aims into the background, and substitute their own aims for them.