“4. Sounds which are both rational and articulate, constituting true speech.
“5. Gestures which do not answer to rational conceptions, but are merely the manifestations of emotions and feelings.
“6. Gestures which do answer to rational conceptions, and are therefore ‘external,’ but not oral manifestations of the verbum mentale.”
To this list of the “Categories of Language” a seventh must be added, to contain all kinds of written signs; but with such obvious addition I assent to the classification, as including all the species that can possibly be included under the genus Language, and therefore as excluding none.
Now the first thing to be noticed is, that the signs made may be made either intentionally or unintentionally; and the next is, that the division of intentional signs may be conveniently subdivided into two classes—namely, intentional signs which are natural, and intentional signs which are conventional.
The subdivision of conventional signs may further be split into those which are due to past associations, and those which are due to inferences from present experience. A dog which “begs” for food, or a parrot which puts down its head to be scratched, may do so merely because past experience has taught the animal that by so doing it receives the gratification it desires; here is no need for reason—i.e. inference—to come into play. But if the animal has had no such previous experience, and therefore could not know by special association that such a particular gesture, or sign, would lead to such a particular consequence, and if under such circumstances a dog should see another dog beg, and should imitate the gesture on observing the result to which it led; or if under such analogous circumstances a parrot should spontaneously depress its head for the purpose of making an expressive gesture,—then the sign might strictly be termed a rational one.
But it is evident that rational signs admit of almost numberless degrees of complexity and elaboration; so that reason itself does not present a greater variety of manifestations in this respect than does the symbolism whereby it is expressed: an algebraical formula is included in the same category of sign-making as the simplest gesture whereby we intentionally communicate the simplest idea. Rational signs, therefore, may be made by gesture, by tone, by articulation, or by writing—using each of these words in its largest sense.[58]
The following schema may serve to show this classification in a diagrammatic form—i.e. the classification which I have myself arrived at, and which follows closely the one given by Mr. Mivart. Indeed, there is no difference at all between the two, save that I have endeavoured to express the distinction between signs as intentional, unintentional, natural, conventional, emotional, and intellectual. The subdivision of the latter into denotative, connotative, denominative, and predicative, will be explained in Chapter VIII.