Science, like all human knowledge, begins with sense-experience. But sense-experience is so diverse and so complicated as to appear almost chaotic. Scientific workers in any field of inquiry keep in touch with one another through the medium of scientific societies, scientific periodicals and other publications. Classification then tended to become more and more objective, or more and more natural, attention being paid more to the character of the things themselves, instead of to their human uses. The vast number of classifications spontaneously made by early man is obvious from the evidence of language. Classification is not only of individuals into classes, but also of classes into wider or higher classes, and of those into still higher classes. The terminological schemes and the statistical methods are important aids to description. The description is, of course, a description of things; but the concise, economic description of the things in a class constitutes the definition of the name of the class.