The best classification of the sundry exhibitions of sign-making faculty which I have met with, is one that is given by Mr. Mivart in his _Lessons from Nature_ (p. 83). This classification, therefore, I will render in his own words. “We may altogether distinguish six different kinds of language:— “1. Sounds which are neither articulate nor rational, such as cries of pain, or the murmur of a mother to her infant. “2. Sounds which are articulate but not rational, such as the talk of parrots, or of certain idiots, who will repeat, without comprehending, every phrase they hear. “3. Sounds which are rational but not articulate, ejaculations by which we sometimes express assent to, or dissent from, given propositions. “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.