edited by Meagan Ayer et al.

Complementary Infinitive

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456. Verbs which imply another action of the same subject to complete their meaning take the Infinitive without a subject accusative. Such are verbs denoting to be able, dare, undertake, remember, forget, be accustomed, begin, continue, cease, hesitate, learn, know how, fear, and the like.

Hōc queō dīcere. (Cat. M. 32)
This I can say.

Mittō quaerere. (Rosc. Am. 53)
I omit to ask.

Vereor laudāre praesentem. (N. D. 1.58)
I fear to praise a man to his face.

Ōrō ut mātūrēs venīre. (Att. 4.1)
I beg you will make haste to come.

Oblīvīscī nōn possum quae volō. (Fin. 2.104)
I cannot forget that which I wish.

Dēsine id mē docēre. (Tusc. 2.29)
Cease to teach me that.

Sīcere solēbat.
She used to say.

Audeō dīcere.
I venture to say.

Loquī posse coepī.
I began to be able to speak.

Note— The peculiarity of the Complementary Infinitive construction is that no subject accusative is in general admissible or conceivable. But some infinitives usually regarded as objects can hardly be distinguished from this construction when they have no subject expressed. Thus volō dīcere and volō mē dīcere mean the same thing (I wish to speak), but the latter is an object infinitive, while the former is not apparently different in origin and construction from queō dīcere (complementary infinitive), and again volō eum dīcere (I wish him to speak) is essentially different from either (cf. § 563.b).

457. Many verbs take either a subjunctive clause or a complementary infinitive, without difference of meaning. Such are verbs signifying willingness, necessity, propriety, resolve, command,prohibition, effort, and the like (cf. § 563)

Dēcernere optābat (Q. C. 3.11.1)
He was eager to decide.

Optāvit ut tollerētur. (Off. 3.94)
He was eager to be taken up.

Oppūgnāre contendit. (B. G. 5.21)
He strove to take by storm.

ut caperet (id. 5.8)
he strove to take

Bellum gerere cōnstituit (id. 4.6)
He decided to carry on war.

Cōnstitueram ut manērem. (Att. 16.10.1)
I had decided to remain.

Note 1— For the infinitive with subject accusative used with some of these verbs instead of a complementary infinitive, see § 563.

Note 2— Some verbs of these classes never take the subjunctive, but are identical in meaning with others which do.

Eōs quōstūtārī dēbent dēserunt. (Off. 1.28)
They forsake those whom they ought to protect.

Aveō pūgnāre. (Att. 2.18.3)
I'm anxious to fight.

a. In poetry and later writers many verbs may have the infinitive, after the analogy of verbs of more literal meaning that take it in prose.

Furit tē reperīre. (Hor. Od. 1.15.27)
He rages to find thee.
[A forcible way of saying cupit457; § 563.b).] 

Saevit exstinguere nōmen. (Ov. M. 1.200)
He rages to blot out the name.

Fuge quaerere (Hor. Od. 1.9.13)
Forbear to ask. (cf. § 450, Note 1)

Parce piās scelerāre manūs. (Aen. 3.42)
Forbear to defile your pious hands.

458. A Predicate Noun or Adjective after a Complementary Infinitive takes the case of the subject of the main verb.

Fierīque studēbam êius prūdentiā doctior. (Lael. 1)
I was eager to become more wise through his wisdom.

Sciō quam soleās esse occupātus (Fam. 16.21.7)
I know how busy you usually are.
(are wont to be)

Brevis esse labōrō, obscūrus fīō (Hor. A. P. 25)
I struggle to be brief, I become obscure.