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

Linguistic sounds, considered as external, physical phenomena have two aspects, the motor and the acoustic.

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

Now the identification of individual sounds by phonetic observation is an artificial way of proceeding.

The search for the symbolic value of phonemes, each taken as a whole, runs the risk of giving rise to ambiguous and trivial interpretations because phonemes are complex entities, bundles of different distinctive features.

It is once again the vexing problem of identity within variety; without a solution to this disturbing problem there can be no system, no classification.

Acoustic phonetics, which is developing and increasing in richness very rapidly, already enables us to solve many of the mysteries of sound, mysteries which motor phonetics could not even begin to solve.