Speech sounds cannot be understood, delimited, classified and explained except in the light of the tasks which they perform in language.

The task is to investigate speech sounds in relation to the meanings with which they are invested, i.e., sounds viewed as signifiers, and above all to throw light on the structure of the relation between sounds and meaning.

Instead of following one another the sounds overlap; a sound which is acoustically perceived as coming after another one can be articulated simultaneously with the latter or even in part before it.

In poetic language, in which the sign as such takes on an autonomous value, this sound symbolism becomes an actual factor and creates a sort of accompaniment to the signified.

At first acoustics attributed to the different sounds only a limited number of characteristic features.

A new era in the physiological investigation of linguistic sounds was opened up by X-ray photography.