The symbol G was a new coinage in the 3rd century B.C. The pronunciation of C throughout the period of classical Latin was that of an unvoiced guttural stop (k).
The sound was that of the unvoiced dental stop. The English t, however, is not dental but alveolar, being pronounced, as d also, not by putting the tongue against the teeth but against their sockets.
In English th represents both the unvoiced sound J as in thin, &c., and the voiced sound 5, which is found initially only in pronominal words like this, that, there, then, those, is commonest medially as in father, bother, smother, either, and is found also finally in words like with (the preposition), both.
Early English used ]' and S indiscriminately for both voiced and unvoiced sounds, in Middle English S disappeared and p was gradually assimilated in form to y, which is often found for it in early printing.
Thus F came to be the representative of the unvoiced labiodental spirant instead of that for the bilabial voiced spirant.
The differentiation of the Roman alphabet from the Greek is brought about (a) by utilizing the digamma for the unvoiced labio dental spirant F; (b) by dropping out the aspirates 0, (I), in the Chalcidian alphabet, whence the Roman is derived) from the alphabet proper and employing them on l as numerals, 0 'y' ?
There is some evidence which seems to point to a pronunciation of the voiced mutes which, like the South German pronunciation of g, d, b, but slightly differentiated them from the unvoiced mutes, so that confusion might easily arise.
The pronunciation of s was originally unvoiced: in English it is often used for the voiced sound as well, compare lose with loose, house with houses.
At the end of words the voiced sound is often written with -s, the unvoiced with -ss as in his and hiss.
In other cases the pronunciation can be ascertained only from the context, as in use, unvoiced for the substantive, voiced for the verb.
In medieval and modern Greek, however, this has become the unvoiced sound represented in English by th in thin, thick, pith.