XXXIX. Now of sentences there are five parts, as Diogenes tells us in his treatise on Voice; and he is followed by Chrysippus. There is the noun, the common noun, the verb, the conjunction, and the article. Antipater adds also quality, in his treatise upon Words and the things expressed by them. And a common noun (προσηγορία) is, according to Diogenes, a part of a sentence signifying a common quality, as for instance, man, horse. But a noun is a part of a sentence signifying a peculiar quality, such as Diogenes, Socrates. A verb is a part of a sentence signifying an uncombined categorem, as Diogenes (ὁ Διογένης) or, as others define it, an element of a sentence, devoid of case, signifying something compound in reference to some person or persons, as, “I write,” “I say.” A conjunction is a part of a sentence destitute of case, uniting the divisions of the sentence. An article is an element of a sentence, having cases, defining the genders of nouns and their numbers, as ὁ, ἡ, τὸ, οἱ, αἱ, τὰ. XL. The excellences of a sentence are five,—good Greek, clearness, conciseness, suitableness, elegance. Good Greek (Ἑλληνισμὸς) is a correct style, according to art, keeping aloof from any vulgar form of expression; clearness is a style which states that which is conceived in the mind in such a way that it is easily known; conciseness is a style which embraces all that is necessary to the clear explanation of the subject under discussion; suitableness is a style suited to the subject; elegance is a style which avoids all peculiarity of expression. Of the vices of a sentence, on the other hand, barbarism is a use of words contrary to that in vogue among the well-educated Greeks; solecism is a sentence incongruously put together. XLI. A poetical expression is, as Posidonius defines it in his introduction on Style, “A metrical or rhythmical diction, proceeding in preparation, and avoiding all resemblance to prose.” For instance, “The vast and boundless earth,” “Th’ expanse of heaven,” are rhythmical expressions; and poetry is a collection of poetical expressions signifying something, containing an imitation of divine and human beings.