ABSTRACT
The significant work of mathematicians on the theory of probability has given rise to the popular misimpression that probability is a purely mathematical concept. Probability is a category of inference that may be sharply distinguished from the kind called necessary, certain, or conclusively demonstrative. The initial probability of any generalization about a newly discovered species of plants or animals would depend on the more general propositions of biology. The overwhelming probability that all men are mortal rests not on the actual number of human deaths any of us have observed, but more on certain wider general propositions about the nature of animal life. It is true, of course, that the latter propositions have a wider range of confirmatory instances; but the distinction between the initial probability of any universal proposition and that which it acquires by confirmation is still a valid one.
