Wisdom from the Early Stoics, Zeno of Citium 30

Elements of language are the four-and-twenty letters. "Letter," however, has three meanings: 

(1) the particular sound or element of speech; 

(2) its written symbol or character; 

(3) its name, as Alpha is the name of the sound "A".

Seven of the letters are vowels, a, e, ē i, o, u, ō, and six are mutes, b, g, d, k, p, t. 

There is a difference between voice and speech; because, while voice may include mere noise, speech is always articulate. 

Speech again differs from a sentence or statement, because the latter always signifies something, whereas a spoken word, as for example βλίτυρι, may be unintelligible—which a sentence never is. 

And to frame a sentence is more than mere utterance, for while vocal sounds are uttered, things are meant, that is, are matters of discourse.

—Diogenes Laërtius, 7.56-57