Along with ‘k’, ‘t’, ‘p’, in the first place, go their nearest kindred, ‘g’, ‘d’, ‘b’. These are their sonant (or vocal, phthongal, intonated) counterparts. In the former, namely, there is no audible utterance, but complete silence, during the continuance of the closure; the antithesis to ‘a’ is absolute; the explosion is their whole sensible substance. In the latter there is, even while the closure lasts, a tone produced by the vibration of the vocal chords, a stream of air sufficient to support vibration for a very brief time being forced up from the lungs into the closed cavity or receiving-box of the pharynx and mouth. This is the fundamental distinction of “surd” and “sonant” sounds; anything else is merely a consequence of this and subordinate to it; the names strong and weak, hard and soft, sharp and flat, and so on, founded […] upon these subordinate characteristics, are to be rejected.
- Whitney (1875), a pag.62-63