I. The Motive of Human Activity.

Man is an organism composed of vital, physical, intellectual, and moral forces. This matter and these forces, which form the individual and the species, can only be preserved and developed by the assimilation, or, to use the economic term, the consumption of materials and forces of like nature. Failing this consumption, their vitality wastes and is finally extinguished. But waste and extinction of vitality cause pain and suffering, and it is the stimulus of pain and suffering which impels man to acquire the materials necessary for the development and preservation of his life. All these materials are present in his environment, air, &c.; and nature gives him a small number free of cost. But with the exception of this minority they must be discovered, acquired, and adapted to the purposes of consumption. Man must be a producer.

Man is also subject to a further necessity, one which is again inherent in his environment. He must defend both life and the means of its support from the attacks of numerous spoilers and agents of destruction. The risks to which he is exposed under this head entail more pain and more endurance.

It is to meet this twofold need—sustenance and self-defence—that man labours, labours to produce the necessaries of consumption and to destroy the agents or elements that menace his security. Labour therefore implies waste of vital force, and this more endurance and more pain. Humanity is, however, compensated by the pleasure and enjoyment which it derives from consuming the materials that support life, and from providing the services that safeguard it. But always, whether there be question of nourishment or self-defence, the pleasure of these actions is bought with a pain. It is an exchange, and, like every other exchange, it may result in a profit or loss. It is profitable when the sum of vitality, acquired or preserved, exceeds the amount of vital force expended in the task. The product may be concrete or one of service, but it is always subject to the costs of production which are inseparable from every expenditure of force.

Excess of expenditure over receipts means, on the other hand, loss, so that man is only stimulated to work when he expects that his receipts will exceed his expenses, that the pleasure will outweigh the pain. The degree of the stimulus naturally varies with the sums involved and the rate of expected profit; the prime motive of human activity, no less than that of all other creatures, is, therefore, the hope of profit. This motive, or motor-power, has been called interest.3