Allen and Greenough's New Latin Grammar for Schools and Colleges
J. B. Greenough, G. L. Kittredge, A. A. Howard, Benj. L. D'Ooge, Ed.

[*] a. Dīcō , faciō , agō, and other common verbs are often omitted in familiar phrases:—

1. quōrsum haec [spectant], what does this aim at?
2. ex ungue leōnem [cōgnōscēs], you will know a lion by his claw.
3. quid multa, what need of many words? (why should I say much?)
4. quid? quod, what of this, that ... ? (what shall I say of this, that ... ?) [A form of transition.]
Aeolus haec contrā; (Aen. 1.76), Æolus thus [spoke] in reply.
5. tum Cotta [inquit], then said Cotta.
dī meliōra [duint]! (Cat. M. 47), Heaven forfend (may the gods grant better things)!
unde [venīs] et quō [tendis]? (Hor. S. 2.4.1), where from and whither bound? [Cf. id. 1.9.62for the full form.]

[*] b. The copula sum is very commonly omitted in the present indica tive and present infinitive, rarely (except by late authors) in the sub junctive:—

1. “tū coniūnx ” (Aen. 4.113) , you [are] his wife.
2. “quid ergō? audācissimus ego ex omnibus ” (Rosc. Am. 2) , what then? am I the boldest of all?
3. “omnia praeclāra rāra ” (Lael. 79) , all the best things are rare.
4. “potest incidere saepe contentiō et comparātiō dē duōbus honestīs utrum honestius ” (Off. 1.152) , there may often occur a comparison of two honorable actions, as to which is the more honorable. [Here, if any copula were expressed, it would be sit , but the direct question would be complete without any.]
5. “accipe quae peragenda prius ” (Aen. 6.136) , hear what is first to be accomplished. [Direct: quae peragenda prius ?]