BOOK XVII. CAP. I.

...[consonants] cannot complete a sound without the help of other parts of speech: so also in words we notice that some are to be spoken by themselves in the likeness of vowels, as especially in imperative verbs, or nouns, or pronouns, or often vocatives, or adverbs, which are added to preceding actions or sentences when we shout "well," "rightly," "eloquently," to those who do or say something opportunely. Other words, however, are those which, in the likeness of consonants, cannot be uttered to the perfection of sense without the help of other parts of speech which they imitate in this as vowels, such as prepositions and conjunctions. For these always co-signify, that is, they signify when joined to others, but not by themselves. And so their signification varies according to the force of those joined to them, as in signifies one thing when joined with the accusative, and another when with the ablative; in urbem into the city and in urbe in the city, 11 in locum into the place and in loco in the place. Conjunctions also are discerned as copulative and disjunctive from other parts of speech which are associated with them, as vel or, aut or; not only disjunctive, but also copulative they are found to be, as Terence in the Eunuch: Vel rex semper maximas mihi Or the king was always giving me the greatest thanks...