In short, I am not endeavouring to argue that the influence of articulation on the development of thought is in any way _magical_. Therefore, the mere fact that certain birds are able to make articulate sounds in itself furnishes no more difficulty to my argument than the fact that they are able to imitate a variety of other sounds. For the _psychological_ use of articulate sounds can only be developed in the presence of many other and highly complex conditions, few if any of which can be shown to obtain among birds. If any existing species of anthropoid ape had proved itself capable of imitating articulate sounds, there might have been a little more force in the apparent difficulty; though even in that case the argument would not have been so strong as in the above parallel with regard to the great exception furnished by bats in the matter of flight. So far, then, as we have yet gone, I do not anticipate that opponents wall find it prudent to take a stand. Seeing that monkeys use their voices more freely than any other animals in the way of intentionally expressive intonation; that all the higher animals make use of gesture signs; that denotative words are (psychologically considered) nothing more than vocal gestures; that, if there is any psychological interval between simple gesticulation and denotative articulation, the interval is demonstrably bridged in the case alike of talking birds, infants, and idiots;—seeing all these things, it is evident that opponents of the doctrine of mental evolution must take their stand, not on the faculty of _articulation_, but on that of _speech_. They must maintain that the mere power of using denotative words implies no real advance upon the power of using denotative gestures; that it therefore establishes nothing to prove the possibility, or even the probability, of articulation arising out of gesticulation; that their position can only be attacked by showing how a sign-making faculty, whether expressed in gesticulation or in articulation, can have become developed into the faculty of predication; that, in short, the fortress of their argument consists, not in the power which man displays of using denotative words, but in his power of constructing predicative propositions. This central position, therefore, we must next attack. But, before doing so, I will close the present chapter by clearly defining the exact meanings of certain terms as they will afterwards be used by me.