The freedom of aesthetic expression is, however, only an intensification of a quality that may belong to any expression. For, in its native character, expression is never merely practical; it brings its own reward in the pleasure of the activity itself. Ordinarily, when a man makes something embodying his need or fancy, or says something that expresses his meaning, he enjoys himself in his doing. There is naturally a generous superfluity in all human behavior. The economizing of it to what is necessary for self-preservation and dominion over the environment is secondary, not primary, imposed under the duress of competition and nature. Only when activities are difficult or their fruits hard to get are they disciplined for the sake of their results alone; then only does their performance become an imperative, and nature and society impose upon them the seriousness and constraint of necessity and law. But whenever nature and the social organization supply the needs of man ungrudgingly or grant him a respite from the urgency of business, the spontaneity of his activities returns. The doings of children, of the rich, and of all men on a holiday illustrate this. Compare, for example, the speech of trade, where one says the brief and needful thing only, with the talk of excursionists, where verbal expression, having no end beyond itself, develops at length and at leisure; where brevity is no virtue and abundant play takes the place of a narrow seriousness. But we have not yet so limited the field of expression that it becomes equivalent to the aesthetic; for not even all of free expression is art. The most important divergent type is science. Science also is expression,--an embodiment in words, diagrams, mathematical symbols, chemical formula, or other such media, of thoughts meant to portray the objects of human experience. Scientific expressions have, of course, a practical function; concepts are "plans of action" or servants of plans, the most perfect and delicate that man possesses. Yet scientific knowledge is an end in itself as well as a utility; for the mere construction and possession of concepts and laws is itself a source of joy; the man of science delights in making appropriate formulations of nature's habits quite unconcerned about their possible uses.