Ancient Greek verbs

Ancient Greek verbs have four moods (indicative, imperative, subjunctive and optative), three voices (active, middle and passive), as well as three persons (first, second and third) and three numbers (singular, dual and plural).

• In the indicative mood there are seven tenses: present, imperfect, future, aorist (the equivalent of past simple), perfect, pluperfect, and future perfect. (The last two, especially the future perfect, are rarely used).
• In the subjunctive and imperative mood, however, there are only three tenses (present, aorist, and perfect).
• The optative mood, infinitives and participles are found in four tenses (present, aorist, perfect, and future) and all three voices.

The distinction of the "tenses" in moods other than the indicative is predominantly one of aspect rather than time.

The different persons of a Greek verb are shown by changing the verb-endings; for example λύω (lúō) "I free", λύεις (lúeis) "you free", λύει (lúei) "he or she frees", etc. There are three persons in the singular ("I", "you (singular)", "he, she, it"), and three in the plural ("we", "you (plural)", "they"). In addition there are endings for the 2nd and 3rd persons dual ("you two", "they both"), but these are only very rarely used.

A distinction is traditionally made between the so-called athematic verbs (also called mi-verbs), with endings affixed directly to the root, and the thematic class of verbs which present a "thematic" vowel /o/ or /e/ before the ending. The endings are classified into primary (those used in the present, future, perfect and future perfect of the indicative, as well as in the subjunctive) and secondary (used in the aorist, imperfect, and pluperfect of the indicative, as well as in the optative).

To make the past tenses of the indicative mood, the vowel ε- (e-), called an "augment", is prefixed to the verb stem, e.g. aorist ἔ-λυσα (é-lusa) "I freed", imperfect ἔ-λυον (é-luon) "I was freeing". This augment is found only in the indicative, not in the other moods or in the infinitive or participle. To make the perfect tense the first consonant is "reduplicated", that is, repeated with the vowel e (λέλυκα (léluka) "I have freed", γέγραφα (gégrapha) "I have written"), or in some cases an augment is used in lieu of reduplication (e.g. ηὕρηκα (hēúrēka) "I have found"). Unlike the augment of past tenses, this reduplication or augment is retained in all the moods of the perfect tense as well as in the perfect infinitive and participle.

The Ancient Greek verbal system preserves nearly all the complexities of Proto-Indo-European (PIE). Ancient Greek also preserves the PIE middle voice and adds a passive voice, with separate forms only in the future and aorist (elsewhere, the middle forms are used).