Part XX 

Language in general includes the following parts: Letter, Syllable, Connecting Word, Noun, Verb, Inflection or Case, Sentence or Phrase. 
A Letter is an indivisible sound, yet not every such sound, but only one which can form part of a group of sounds. For even brutes utter indivisible sounds, none of which I call a letter. The sound I mean may be either a vowel, a semivowel, or a mute. A vowel is that which without impact of tongue or lip has an audible sound. A semivowel that which with such impact has an audible sound, as S and R. A mute, that which with such impact has by itself no sound, but joined to a vowel sound becomes audible, as G and D. These are distinguished according to the form assumed by the mouth and the place where they are produced; according as they are aspirated or smooth, long or short; as they are acute, grave, or of an intermediate tone; which inquiry belongs in detail to the writers on meter. 
A Syllable is a nonsignificant sound, composed of a mute and a vowel: for GR without A is a syllable, as also with A- GRA. But the investigation of these differences belongs also to metrical science. 
A Connecting Word is a nonsignificant sound, which neither causes nor hinders the union of many sounds into one significant sound; it may be placed at either end or in the middle of a sentence. Or, a nonsignificant sound, which out of several sounds, each of them significant, is capable of forming one significant sound- as amphi, peri, and the like. Or, a nonsignificant sound, which marks the beginning, end, or division of a sentence; such, however, that it cannot correctly stand by itself at the beginning of a sentence- as men, etoi, de. 
A Noun is a composite significant sound, not marking time, of which no part is in itself significant: for in double or compound words we do not employ the separate parts as if each were in itself significant. Thus in Theodorus, ‘god-given,’ the doron or ‘gift’ is not in itself significant. 
A Verb is a composite significant sound, marking time, in which, as in the noun, no part is in itself significant. For ‘man’ or ‘white’ does not express the idea of ‘when’; but ‘he walks’ or ‘he has walked’ does connote time, present or past. 
Inflection belongs both to the noun and verb, and expresses either the relation ‘of,’ ‘to,’ or the like; or that of number, whether one or many, as ‘man’ or ‘men’; or the modes or tones in actual delivery, e.g., a question or a command. ‘Did he go?’ and ‘go’ are verbal inflections of this kind. 
A Sentence or Phrase is a composite significant sound, some at least of whose parts are in themselves significant; for not every such group of words consists of verbs and nouns- ‘the definition of man,’ for example- but it may dispense even with the verb. Still it will always have some significant part, as ‘in walking,’ or ‘Cleon son of Cleon.’ A sentence or phrase may form a unity in two ways- either as signifying one thing, or as consisting of several parts linked together. Thus the Iliad is one by the linking together of parts, the definition of man by the unity of the thing signified.
Part XXI
Words are of two kinds, simple and double. By simple I mean those composed of nonsignificant elements, such as ge, ‘earth.’ By double or compound,those composed either of a significant and nonsignificant element (though within the whole word no element is significant), or of elements that are both significant. A word may likewise be triple, quadruple, or multiple in form, like so many Massilian expressions, e.g., ‘Hermo-caico-xanthus [who prayed to Father Zeus].’ 
Every word is either current, or strange, or metaphorical, or ornamental, or newly-coined, or lengthened, or contracted, or altered. 
By a current or proper word I mean one which is in general use among a people; by a strange word, one which is in use in another country. Plainly, therefore, the same word may be at once strange and current, but not in relation to the same people. The word sigynon, ‘lance,’ is to the Cyprians a current term but to us a strange one. 
Metaphor is the application of an alien name by transference either from genus to species, or from species to genus, or from species to species, or by analogy, that is, proportion. Thus from genus to species, as: ‘There lies my ship’; for lying at anchor is a species of lying. From species to genus, as: ‘Verily ten thousand noble deeds hath Odysseus wrought’; for ten thousand is a species of large number, and is here used for a large number generally. From species to species, as: ‘With blade of bronze drew away the life,’ and ‘Cleft the water with the vessel of unyielding bronze.’ Here arusai, ‘to draw away’ is used for tamein, ‘to cleave,’ and tamein, again for arusai- each being a species of taking away. Analogy or proportion is when the second term is to the first as the fourth to the third. We may then use the fourth for the second, or the second for the fourth. Sometimes too we qualify the metaphor by adding the term to which the proper word is relative. Thus the cup is to Dionysus as the shield to Ares. The cup may, therefore, be called ‘the shield of Dionysus,’ and the shield ‘the cup of Ares.’ Or, again, as old age is to life, so is evening to day. Evening may therefore be called, ‘the old age of the day,’ and old age, ‘the evening of life,’ or, in the phrase of Empedocles, ‘life’s setting sun.’ For some of the terms of the proportion there is at times no word in existence; still the metaphor may be used. For instance, to scatter seed is called sowing: but the action of the sun in scattering his rays is nameless. Stillthis process bears to the sun the same relation as sowing to the seed. Hence the expression of the poet ‘sowing the god-created light.’ There is another way in which this kind of metaphor may be employed. We may apply an alien term, and then deny of that term one of its proper attributes; as if we were to call the shield, not ‘the cup of Ares,’ but ‘the wineless cup’. 
A newly-coined word is one which has never been even in local use, but is adopted by the poet himself. Some such words there appear to be: as ernyges, ‘sprouters,’ for kerata, ‘horns’; and areter, ‘supplicator’, for hiereus, ‘priest.’ 
A word is lengthened when its own vowel is exchanged for a longer one, or when a syllable is inserted. A word is contracted when some part of it is removed. Instances of lengthening are: poleos for poleos, Peleiadeo for Peleidou; of contraction: kri, do, and ops, as in mia ginetai amphoteron ops, ‘the appearance of both is one.’ 
An altered word is one in which part of the ordinary form is left unchanged, and part is recast: as in dexiteron kata mazon, ‘on the right breast,’ dexiteron is for dexion. 

Nouns in themselves are either masculine, feminine, or neuter. Masculine are such as end in N, R, S, or in some letter compounded with S- these being two, PS and X. Feminine, such as end in vowels that are always long, namely E and O, and- of vowels that admit of lengthening- those in A. Thus the number of letters in which nouns masculine and feminine end is the same; for PS and X are equivalent to endings in S. No noun ends in a mute or a vowel short by nature. Three only end in I- meli, ‘honey’; kommi, ‘gum’; peperi, ‘pepper’; five end in U. Neuter nouns end in these two latter vowels; also in N and S.
Poetics By Aristotle