This primordial babbling is wonderfully rich and varied. According to Preyer it contains most, if not all the sounds which are afterwards used in speaking, and among these some which cause much difficulty later on. It is thus a wondrous contrivance of nature by which the child is made to rehearse months beforehand for the difficult performances of articulate speech. It is a preliminary trying of the vocal instrument throughout the whole of its register. Though nurses are apt to fancy that in this pretty babbling the infant is talking to itself there is no reason to think that it amounts even to a rudiment of true speech. To speak is to use a sound intentionally as the sign of an idea. The babbling baby of five months cannot be supposed to be connecting all these stray sounds with ideas, if indeed it can be said to have as yet any definite ideas. The only signification which this primitive articulation can have is emotional. Undoubtedly, as we have seen, it grows out of expressive cries. Even the happy bubblings over of vowel sounds as the child lies on his back and ‘crows,’ may be said to be expressive of his happiness like the movements of arms and legs which accompany it. Yet it would be an exaggeration to suppose that the elaborate phonation is merely expressive, that all the manifold and subtle changes of sound are due to obscure variations of feeling. The true explanation seems to be that the appearance of this infantile babbling, just like that of the movements of the limbs which accompany it, is the result of changes in the nervous system. As the centres of vocalisation get developed, motor impulses begin to play on the muscles of throat, larynx, and, later on, lips, tongue, etc., and in this way a larger and larger variety of sound and sound-combination is produced. Such phonation is commonly described as impulsive. It is instinctive, that is to say, unlearnt, and due to congenital nervous connexions; and at best it can only be said to express in its totality a mood or relatively permanent state of feeling.