of normal speech itself, is that each element (letter or written word) in the system corresponds to a specific element (sound or sound-group or spoken word) in the primary system.  Written language is thus a point-to-point equivalence, to borrow a mathematical phrase, to its spoken counterpart.  The written forms are secondary symbols of the spoken ones—­symbols of symbols—­yet so close is the correspondence that they may, not only in theory but in the actual practice of certain eye-readers and, possibly, in certain types of thinking, be entirely substituted for the spoken ones.  Yet the auditory-motor associations are probably always latent at the least, that is, they are unconsciously brought into play.  Even those who read and think without the slightest use of sound imagery are, at last analysis, dependent on it.  They are merely handling the circulating medium, the money, of visual symbols as a convenient substitute for the economic goods and services of the fundamental auditory symbols.

The possibilities of linguistic transfer are practically unlimited.  A familiar example is the Morse telegraph code, in which the letters of written speech are represented by a conventionally fixed sequence of longer or shorter ticks.  Here the transfer takes place from the written word rather than directly from the sounds of spoken speech.  The letter of the telegraph code is thus a symbol of a symbol of a symbol.  It does not, of course, in the least follow that the skilled operator, in order to arrive at an understanding of a telegraphic message, needs to transpose the individual sequence of ticks into a visual image of the word before he experiences its normal auditory image.  The precise method of reading off speech from the telegraphic communication undoubtedly varies widely with the individual.  It is even conceivable, if not exactly likely, that certain operators may have learned to think directly, so far as the purely conscious part of the process of thought is concerned, in terms of the tick-auditory symbolism or, if they happen to have a strong natural bent toward motor symbolism, in terms of the correlated tactile-motor symbolism developed in the sending of telegraphic messages.

Still another interesting group of transfers are the different gesture languages, developed for the use of deaf-mutes, of Trappist monks vowed to perpetual silence, or of communicating parties that are within seeing distance of each other but are out of earshot.  Some of these systems are one-to-one equivalences of the normal system of speech; others, like military gesture-symbolism or the gesture language of the Plains Indians of North America (understood by tribes of mutually unintelligible forms of speech) are imperfect transfers, limiting themselves to the rendering of such grosser speech elements as are an imperative minimum under difficult circumstances.  In these latter systems, as in such still more imperfect symbolisms as those used at sea or in the woods, it may be contended that language no longer properly plays a part but that the ideas are directly conveyed by an utterly unrelated symbolic process or by a quasi-instinctive imitativeness.  Such an interpretation would be erroneous.  The intelligibility of these vaguer symbolisms can hardly be due to anything but their automatic and silent translation into the terms of a fuller flow of speech.