In colloquial and poetic language, common verbs like dīcō, faciō, agō and the like are often omitted.
- What does this aim at: quō hōc [spectat]?
- You will know a lion by his claws: ex ungue leōnem [cōgnōscēs].
- What shall I say of this: quid [dē hōc dicam]?
- The songstress thus spoke in replay: haec contrā cantrix [inquit].
- Then Cotta said: tum Cotta [inquit].
- Where are you from, and where are you of to: unde [venīs] et quō [tendis]?
Sum, as a copula, is omitted quite frequently where it is a present indicative or present infinitive:
- You are his wife: tū coniūnx [es].
- What need of many words: quid multa [verbōrum est]?
- What then? Am I the boldest of all: quid ergō [est]? audācissimus ego ex omnibus [sum]?
- The best things are rare: omnia praeclāra rāra [sunt]?
- Hear first what must be accomplished: accipe quae peragenda prius [sunt].
As you might imagine, omission of sum will be especially popular in proverbs and sententiae, where clever identities and definitions are made all the time, making a est or a sunt all too predictable.
The Essential AG: 319a