Scientific questions about speech sounds

One of the scientific questions that need to be asked about language is: what is a possible speech sound? Humans can physically produce many more kinds of sounds than are used in language. No language employs hand-clapping, finger-snapping, or vibrations of air between the hand and cheek caused by release of air from the mouth when obstructed by the palm of the hand (though such a sound can easily communicate an attitude). A goal of a scientific theory of language is to systematize such facts and explain them; thus we have discovered one limitation on language sound and its modality – language sounds are produced exclusively within the mouth and nasal passages, in the area between the lips and larynx.

Even staying within the vocal tract, languages also do not, for example, use whistles or inhalation to form speech sounds, nor is a labiolingual trill (a.k.a. “the raspberry”) a speech sound in any language. It is important to understand that even though these various odd sounds are not language sounds, they may still be used in communication. The “raspberry” in American culture communicates a contemptuous attitude; in parts of coastal East Africa and Scandinavia, inhaling with the tongue in the position for schwa expresses agreement. Such noises lie outside of language, and we never find plurality indicated with these sounds, nor are they surrounded by other sounds to form the word dog. General communication has no systematic limitations short of anatomical ones, but in language, only a restricted range of sounds are used.

The issue of possible speech sounds is complicated by manual languages such as American Sign Language. ASL is technically not a counterexample to a claim about modality framed in terms of “speech sounds.” But it is arbitrary to declare manual language to be outside the theory of language, and facts from such languages are relevant in principle. Unfortunately, knowledge of the signed languages of the world is very restricted, especially in phonology. Signed languages clearly have syntax: what isn’t clear is what they have by way of phonologies. Researchers have only just begun to scratch the surface of sign language phonologies, so unfortunately we can say nothing more about them here.

The central question is: what is the basis for defining possible speech sounds? Do we use our “speech anatomy” in every imaginable way, or only in certain well-defined ways?