But let us look at a science less exact than astronomy. They have to use the word probably, which the astronomers do not need to use when talking about the eclipses of Jupiter's satellites. A heavy downpour of rain in the upper Thames valley, or a strong north-east wind in the German Ocean, may make the tides at London Bridge differ a good deal from what had been expected. The laws of economics are to be compared with the laws of the tides, rather than with the simple and exact law of gravitation. For the actions of men are so various and uncertain, that the best statement of tendencies, which we can make in a science of human conduct, must needs be inexact and faulty.
Life is human conduct, and the thoughts and emotions that grow up around it.
And since we must form to ourselves some notions of the tendencies of human action, our choice is between forming those notions carelessly and forming them carefully. Economic laws, or statements of economic tendencies, are those social laws which relate to branches of conduct in which the strength of the motives chiefly concerned can be measured by a money price. There is thus no hard and sharp line of division between those social laws which are, and those which are not, to be regarded also as economic laws. And following our definition of an economic law, we may say that the course of action which may be expected under certain conditions from the members of an industrial group is the normal action of the members of that group relatively to those conditions. When we talk of a Good man or a Strong man, we refer to excellence or strength of those particular physical mental or moral qualities which are indicated in the context.