[USE OF CASES WITH PREPOSITIONS.]
[1401.] Two cases, the accusative and the ablative, are used with prepositions.
[1402.] Prepositions were originally adverbs which served to define more exactly the meaning of a verb.
Thus, endo, in, on, the older form of in, is an adverb, in an injunction occurring in a law of the Twelve Tables, 451 B.C., manum endo iacitō, let him lay hand on. Similarly, trāns, over, in trānsque datō, and he must hand over, i.e. trāditōque.
[1403.] In the course of time such adverbs became verbal prefixes; the verbs compounded with them may take the case, accusative or ablative, required by the meaning of the compound. Thus, amīcōs adeō, I go to my friends ([1137]); urbe exeō, I go out of town ([1302]).
[1404.] For distinctness or emphasis, the prefix of the verb may be repeated before the case: as, ad amīcōs adeō; ex urbe exeō. And when it is thus separately expressed before the case, it may be dropped from the verb: as, ad amīcōs eō; ex urbe eō.
[1405.] The preposition thus detached from the verb becomes an attendant on a substantive, and serves to show the relation of the substantive in a sentence more distinctly than the case alone could.
[1406.] A great many adverbs which are never used in composition with a verb likewise become prepositions: as, apud, circiter, īnfrā, iūxtā, pōne, propter, &c., &c. The inflected forms of substantives, prīdiē, postrīdiē ([1413]), tenus ([1420]), and fīnī ([1419]), are also sometimes used as prepositions. And vicem ([1145]), causā, grātiā, nōmine, ergō ([1257]), resemble prepositions closely in meaning.
[1407.] A trace of the original adverbial use of prepositions is sometimes retained, chiefly in poetry, when the prefix is separated from its word by what is called Tmesis: as, īre inque gredī, i.e. ingredīque, Lucr. 4, 887, to walk and to step off. per mihī̆ mīrum vīsum est, DO. 1, 214, passing strange it seemed to me.
[1408.] Even such words as are used almost exclusively as prepositions sometimes retain their original adverbial meaning also: as, adque adque, E. in Gell. 10, 29, 2, and up and up, and on and on, or and nearer still and still more near. occīsīs ad hominum mīlibus quattuor, 2, 33, 5, about four thousand men being killed. susque dēque, Att. 14, 6, 1, up and down, topsy turvy, no matter how.