Play (n.) is contrasted with adult work. It is infantile and primitive, unconscious rather than conscious, the product of impulse rather than reason. The developing individual has to learn to give it up as he moves toward maturity. In adults it is regressive.
Play (n.) is somewhat counterintuitively, a very serious activity for children, drawing on large amounts of emotion. Its opposite is not what is serious, but what is real.
Play (n.) is ruled by one wish in children: to be grown-up and do what grown-ups do; by repeating what struck them in life they make themselves masters of the situation.
Play (n.) is a motor hallucination of the satisfied wish — not resignation to impotence but the result of the paramount virtue children and primitives ascribe to their wishes.
Play (n.) lets the child master what hurt him: every distressing impression gets replayed, now done rather than suffered.
Play (n.) can frighten: many adults playfully threaten to gobble up or cut open the child they romp with, which can frighten children badly.
Play (n.) is the child's version of creative writing: he builds a world of his own, or rearranges his world in a way that pleases him, and takes it very seriously.
Play (n.) answers passive with active: the child examined by the doctor plays doctor on a younger sibling.