Professor Cooley, in his chapters on communication,1 speaks of it as a mechanism. A process must have some kind of medium in which to go on, and the medium through which mind stimulates mind is the system of symbols, partly natural but mostly conventional. This system of symbols repeats the world of thought, though of course imperfectly, somewhat as the world of thought repeats the world of objective reality. Cooley1 relates the incident in the life of Helen Keller, how at the belated age of seven she suddenly discovered the world of symbols.

1 Cooley, Social Organization, Part II.

An elaborate classification of the forms of communication may not be worth while, but we may at least recognize two forms, verbal and non-verbal, together with certain complex forms which combine both of these.