(Roman Jakobson and Linda R. Waugh)
In the Greek philosophical literature indivisible sound units capable of forming meaningful strings were termed STOICHEIA, 'the underlying primes of sounds and letters'. The sound shape of language and correspondingly its alphabet were viewed as a joint coherent system with a limited number of discrete and interconnected formal units. This concept proved to be so persuasive that Democritus (fragment A6; cf. Diels and Wilpert) and his adherent Lucretius, in searching for an analogy which might confirm their theory of the atomic structure of the physical universe, cited STOICHEIA as the minimal components of speech.
Just as in Antiquity the term STOICHEION, used originally for linguistic elemental units, was extended to the physical world, in a similar way, but reversely, linguistic theory of the past hundred years in its quest for the ultimate constituents has appealed in turn to the model of atomic physics.