But they all aim at exactness. That is they all aim at precipitating the result of a multitude of observations into provisional statements, which are sufficiently definite to be brought under test by other observations of nature. These statements, when first put forth, seldom claim a high authority. But after they have been tested by many independent observations, and especially after they have been applied successfully in the prediction of coming events, or of the results of new experiments, they graduate as laws. Let us then consider more closely the nature of economic laws, and their limitations.
Every cause has a tendency to produce some definite result if nothing occurs to hinder it.
The law of gravitation states how any two things attract one another. The law of gravitation is therefore a statement of tendencies. It is a very exact statement - so exact that mathematicians can calculate a Nautical Almanac, which will show the moments at which each satellite of Jupiter will hide itself behind Jupiter. 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.