The Ancient Greek infinitive is a non-finite verb form, sometimes called a verb mood, with no endings for person or number, but it is (unlike in Modern English) inflected for tense and voice (for a general introduction in the grammatical formation and the morphology of the Ancient Greek infinitive see here and for further information see these tables).

It is used mainly to express acts, situations and in general "states of affairs" that are depended on another verb form, usually a finite one.

It is a non declinable nominal verb form equivalent to a noun, and expresses the verbal notion abstractly; used as a noun in its main uses, it has many properties of it, as it will be seen below, yet it differs from it in some respects:Kühner, Raphael. Grammar of the Greek language for the use in high schools and colleges. (Translated by B. B. Edwards and S. H. Taylor). 1844. Pp. 449 ff.

(a) When used with no article, and in its major uses (subject/object), it can normally only be equivalent to either a nominative or an accusative case; used with the article, it may be in any case (nominative, genitive, dative and accusative). (b) It shows morphological formation according to aspect, voice (active, middle, passive) and tense (only the future infinitive). (c) It retains some verbal syntactic features: it governs the same oblique case (its object) as the verb to which it belongs, and it may have a subject of its own, in accusative case (See the section accusative and infinitive below). (d) It is modified by adverbials and not by adjectives.

Uses Ancient Greek has both (a) the infinitive with the article (articular infinitive), for example "doing wrong, wrong-doing" and (b) the infinitive without the article, for example "to do wrong".

The infinitive with the article The articular infinitiveHerbert Weir Smyth §§ 2025-2037 corresponds to a cognate verbal noun (in singular number only). It is preceded by the neuter singular article (, , ) and has the character and function of both a noun and a verbal form. It can be used in any case (nominative, genitive, dative, accusative) and thus participate in a construction just like any other noun: it can be subject, object (direct or indirect), predicative expression (rarely), or it may also serve as an apposition; it may have an adnominal (e.g. to be in a genitive construction as a possessive or objective genitive etc.) or an adverbial use (e.g. it can form a genitive that denotes cause etc.); it may form an exclamation (in poetry); it can also be the complement (object) of a preposition in any oblique case and denote many adverbial relations; finally, if in the genitive case, it can denote purpose, oftener a negative one.

Demosthenes, 12 (Philippi epistula), 4 (The articular infinitive τὸ παρανομεῑν is somehow equivalent to the noun ἡ παρανομία "the unlawfulness", and here in nominative case serves as the subject of the verb δοκεῖ "seem, be-considered") To transgress the laws (= the act of transgressing the laws) against a herald and against ambassadors is considered by all other men to be impious.

(as a predicative nominal in nominative), Plato, Gorgias, 483c (as a nominative apposition to the demonstrative pronoun ) This is (the definition of) injustice: to seek to have more than other people.

Xenophon, Oeconomicus, 14.7 (as a dative complement of the verb ) Seeing that the lawful become richer than the unlawful, many, even though they are greedy of gain, very easily persist in not doing unjust acts.

Dinarchus, 1 (In Demosthenem), 113 (as a dative complement of the preposition , denoting cause) He takes pride in being able to speak (= ...in his ability to speak)

Plato, Gorgias, 489a (τὸ ἀδικεῖν is the subject of the verb ὲστίν and τοῦ ἀδικεῖσθαι serves as a genitive of comparison depended on the comparative degree adjective ) Wrong-doing is not only by convention more base than suffering it, but also by nature.

Thucydides, Historiae, 2.32 (as a genitive of purpose) Αtalante was fortified by the Athenians... to prevent pirates from ravaging Euboea.

In all the preceding passages the articular infinitive is in the present tense stem; yet this is by no means a rule, since it can be used in any tense stem, denoting a variety of aspectual differences (For more details see below the discussion about the present and aorist dynamic infinitive).

Infinitive without the article The infinitive without the article is of two sorts and has two discrete uses: the dynamic infinitive and the declarative infinitive.Madvig, J.N., Syntax der griechishen Sprache, besonders der attishen Sprachform, für Shulen. Braunsweig 1847, pp. 187ff.Rijksbaron, Albert. The syntax and semantics of the verb in classical Greek. The University of Chicago Press, 2006, pp. 96ff., §§31ff. Traditionally they are said to be used not in indirect discourse and in indirect discourse respectively, yet this terminology is misleading; for infinitives of both sorts may be used in indirect discourse transformations (for example one may say (a) "I claimed that he will/would undertake an expedition" or (b) "I told/ advised him to undertake/that he should undertake an expedition", where indirect discourse, one way and another, is employed: direct discourse for (a) "He will undertake...", and for (b) "Undertake/you should undertake..."). In ancient Greek both expressions can be constructed upon an infinitival phrase: (a) ἔφην [τοῦτον ἐκστρατεύσεσθαι], direct speech οῠτος ἐκστρατεύσεται (a future declarative infinitive representing a future indicative), (b) ἔφην αὐτῷ [ἐκστρατεύσασθαι], direct speech ἐκστράτευσαι (an aorist dynamic infinitive representing a 2nd person singular imperative); about the presence and/or case of the infinitival subject more are to be said bellow.

Dynamic infinitive

A so-called dynamic infinitive may be governed by verbs of will or desire to do something ( or "to be willing, wish to", "pray, wish for", "pray against, imprecate curse to", "choose, prefer to", "to be about to, or: delay to", "urge, command to", "order to", "vote to", "allow to", "beg to" etc.), verbs of will or desire not to do anything ( "fear to", "be afraid to", "abstain from doing", "be ashamed to", "forbid to", "hinder, prevent" etc.) and verbs or verbal expressions denoting ability, fitness, necessity, capacity, etc. (, "be able to", , "know how to", "learn to", , "I am able to", "it is fair/right to", "it is necessary to", "it is time to" etc.). It can also be found after adjectives (and sometimes derived adverbs) of kindred meaning ( "skillful", "able", "able", "sufficient, capable" etc.). It stands as the object (direct or indirect) of such verbs or verbal expressions, or it serves as the subject if the verb/the verbal expression is used impersonally; it also defines the meaning of an adjective almost as an accusative of respect. An infinitive of this kind denotes only aspect or stage of action, not actual tense,William Watson Goodwin, Syntax of the Moods and Tenses of the Greek Verb. Cambridge University Press, Third edition, 1867, p.12 § 15; p. 22 § 18.2.b; p. 30 § 23.1; p. 212 § 106, REMARK. Henceforth quotations from the online version: § 96ff. § 87. and can be in any tense stem (mostly in the present and aorist (see also here), the perfect being rare enough) except the future one; only the verb "I am about to" may exceptionally take a dynamic future infinitive.William Watson Goodwin, Syntax of the Moods and Tenses of the Greek Verb § 73.

The difference between the present and the aorist infinitive of this sort is aspect or stage of action, not the tense —despite their tense stem, such infinitives always have a future reference, because of the volitive meaning of their governing verb. More specifically, an infinitive in the present verb stem lays stress on "the process or course of the state of affairs", and in many cases has "an immediative" semantic force, while an infinitive in the aorist verb stem lays stress "on the completion of the state of affairs, expressing a well-defined or well-delineated state of affairs".Rijksbaron, Albert. The syntax and semantics of the verb in classical Greek. University of Chicago Press, 2006, pp. 102-103, §33.1, and pp. 44–45, §16.2.

Present dynamic infinitive (continuing stage of action):

I want (for) you to go to Athens (=every time, or=to start/keep going to Athens etc.).

It is necessary to fight (= to start/keep fighting).

Aorist dynamic infinitive (completed stage of action):

I want (for) you to go to Athens. (just once, a simple and sole occurrence of going)

.Plato, Apologia Socratis 22b I'm ashamed to tell you the truth. (just once, a simple occurrence of telling, as in the previous example)

Analogous aspectual distinctions between the present and aorist verbal stem are present also in the use of finite moods as the imperative and the subjunctiveWilliam Watson Goodwin, "Syntax of the moods and tenses of the Greek verb",§ 89 and even the optative of wishesWilliam Watson Goodwin, "Syntax of the moods and tenses of the Greek verb"§ 94 in independent clauses.Rijksbaron, Albert. The syntax and semantics of the verb in classical Greek. The University of Chicago Press, 2006, pp. 39-48, §§13-16 So, in cases as those presented in the following examples, a dynamic infinitive somehow recalls a corresponding finite mood expressing will or desire, pray or curse, exhortation or prohibition etc. and indirect discourse is from one aspect employed:

Thucydides, Historiae, 6.102.2 (aorist dynamic infinitive) He ordered the servants to set fire to the war engines and timber. Direct speech form: (2nd plural person, aorist imperative mood) "Set fire to the war engines and timber."

Plato, Respublica, 394a (aorist dynamic infinitive) He prayed (to Apollo) that the Achaeans should suffer a penalty for his tears by means of his (:the god's) shafts. Direct speech form: . "Apollo, may the Achaeans suffer a penalty for my tears by means of your shafts". (aorist optative of wish, expressing curse)

Declarative infinitive

A so-called declarative infinitiveRijksbaron, Albert. The syntax and semantics of the verb in classical Greek. University of Chicago Press, 2006, pp. 106ff., §33.2. (see also declarative sentence) is mostly used in connexion with verbs (or verbal expressions) of saying, thinking and (sometimes) perceiving such as , , , , , , etc. and it is usually used in oratio obliqua (in indirect speech or indirect discourse). The latter means that it represents a corresponding finite verb form of the oratio recta (of the direct speech or discourse),William Watson Goodwin. Syntax of the moods and tenses of the Greek verb §§ 115, 683. thus a declarative infinitive denotes both tense and aspect or stage of action. But the present infinitive represents either a present indicative or an imperfect one,William Watson Goodwin. Syntax of the moods and tenses of the Greek verb , § 119 and a perfect infinitive either a perfect indicative or a pluperfect one.William Watson Goodwin. Syntax of the moods and tenses of the Greek verb, § 123 A declarative infinitive with the particle is also the representative of a potential indicative or potential optative of the corresponding tense.

Xenophon, Hellenica, 2.3.24 (Present infinitive = present indicative) Men of the Senate, if anyone among you thinks that more people than the situation requires are being put to death, let him give consideration to the fact that these things happen wherever any system of government is transformed. Direct form: "More people are being put to death than the situation requires".

Plato, Symposium, 176a (Aorist infinitive = aorist indicative; present infinitive = imperfect indicative)For the difference between the aorist and the imperfect in narration see: William Watson Goodwin, Syntax of the moods and tenses of the Greek verb, § 56 He said that they made drink offerings to the gods and they started betaking themselves to drinking.