533. The Purpose of an action is expressed in Latin in various ways; but never (except in idiomatic expressions and rarely in poetry) by the simple Infinitive as in English (§ 460).
The sentence, they came to seek peace, may be rendered—
(1) vēnērunt ut pācem peterent. [Final clause with ut (§ 531. 1).]
(2) vēnērunt quī pācem peterent. [Final clause with Relative (§ 531. 2).]
(3) [vēnērunt ad petendum pācem.] Not found with transitive verbs (§ 506 , N.2), but cf. ad pārendum senātuī. [Gerund with ad (§ 506).]
(4) vēnērunt ad petendam pācem. [Gerundive with ad (§ 506).]
(5) vēnērunt pācem petendī causā (grātiā). [Gen. of Gerund with causā (§ 504. b).]
(6) vēnērunt pācis petendae causā (grātiā). [Gen. of Gerundive with causā (§ 504 . b).]
(7) vēnērunt pācem petītūrī. [Future participle (§ 499. 2); in later writers.]
(8) vēnērunt pācem petītum. [Supine in -um (§ 509 ).]
These forms are not used indifferently, but—
a. The usual way of expressing purpose is by ut (negative nē), unless the purpose is closely connected with some one word, in which case a relative is more common:—
lēgātōs ad Dummnorīgem mittunt, ut eō dēprecātōre ā Sēquanīs impetrārent (B. G. 1.9), they send envoys to Dumnorix, in order through his intercession to obtain (this favor) from the Sequani.
mīlitēs mīsit ut eōs quī fūgerant persequerentur (id. 5.10), he sent the soldiers to follow up those who had fled.
Cūriō praemittit equitēs quī prīmum impetum sustineant (B. C. 2.26), Curio sends forward cavalry to withstand the first attack.
b. The Gerund and Gerundive constructions of purpose are usually limited to short expressions, where the literal translation, though not the English idiom, is nevertheless not harsh or strange.
c. The Supine is used to express purpose only with verbs of motion, and in a few idiomatic expressions (§ 509).
d. The Future Participle used to express purpose is a late construction of inferior authority (§ 499. 2).
For the poetical Infinitive of Purpose, see § 460. c. For the Present Participle in a sense approaching that of purpose, see § 490. 3.