Aside from its social significance as the almost exclusive means of communication among the members of society, language has its significance for purely individual mental activity and mental growth. This has already been referred to above. Language makes possible an almost unlimited refinement of abstract thought, a complete analysis of the data of perceptual, ideational, and affective life into their elements, and the construction out of them of new concepts, first according to their similarities, then according to purposes. Such concepts as acceleration, pitch of tone, irrational number, atomic heat, justice, bliss, would be impossible without language. To the invention of such abstract concepts mankind owes its subjugation of nature. It is difficult to think of the exact manner in which bodies fall when they are dropped; some fall slowly, others with great velocity, some do not fall at all, but rise. But think of them as being in space from which the air has been exhausted, and apply the concept of acceleration. At once the matter is very simple, and it includes even the heavenly bodies with which we never come in direct contact: all bodies fall with _constant acceleration_. This is but one of innumerable instances. Practically all laws of physics, chemistry, philology, psychology, and all the other sciences are stated in terms of highly abstract concepts. Imagine, for example, the sine or tangent of an angle, electromotor force, molecular weight, consonants and vowels, intensity of sensation. None of these abstract concepts and none of the laws in which they appear could have been invented without the aid of language. How restricted, further, would be our knowledge without language! How limited the exchange of opinions! Think of such a phrase as “the events of the last thirty years.” What a multitude of ideas is suggested by it in the most economical manner! Few of these ideas actually become conscious; but all of them are made ready to serve if their services should be needed.