Fourth-Conjugation Deponents

Fourth-conjugation deponents combine a recognizable ī-stem with passive-form endings and normally active meaning. In mentior, mentīrī, mentītus sum “lie,” for example, mentītur means “he or she lies,” while mentītus est means “he lied” or “has lied.” The morphology resembles a passive, but the subject remains the performer of the action.

For an English-speaking learner, the safest route is not “How do I translate ‘lie’?” but “Which principal part supplies this form?” The infinitive mentīrī identifies the fourth conjugation; the first principal part predicts the present; the third supplies mentīt- for the perfect system. Translation comes after that structural analysis.

Recognizing the -īrī infinitive

The clearest diagnostic is the present infinitive. Fourth-conjugation deponents end in -īrī, whereas third-conjugation deponents have -ī: compare mentīrī “to lie” with sequī “to follow.”

All are ordinary (neutral Classical prose) lexemes, though individual meanings have their own syntactic preferences. Potior, for example, commonly governs an ablative and also occurs with a genitive; deponency itself does not determine that case.

Present indicative: passive shape, active syntax

The present indicative of mentior follows the fourth-conjugation passive pattern:

The ending still carries person and number. Latin does not need an expressed pronoun unless contrast or emphasis makes it useful. Nor does -tur create passive syntax: the person denoted by the subject tells the lie.

Experīrī is a complementary infinitive after volumus. Its passive-looking ending does not mean “to be tried,” and its object omnia remedia remains accusative.

Imperfect, future, and present subjunctive

Fourth-conjugation deponents use -iēbā- in the imperfect: mentiēbar, mentiēbāris, mentiēbātur. Their future uses -ia-/-iē- plus passive endings: mentiar, mentiēris, mentiētur, mentiēmur, mentiēminī, mentientur. The present subjunctive uses -iā- after the first-person form: mentiar, mentiāris, mentiātur, mentiāmur, mentiāminī, mentiantur.

The macron separates useful forms on the page: present mentīris has the long stem vowel, while future mentiēris has the future marker -iē-. In unmacronized authentic texts, syntax and context must do that work.

The first-person singular mentiar can be either future indicative or present subjunctive. As with third-conjugation sequar, the surrounding construction determines mood. A future condition supports the indicative; a fear clause or purpose clause supports the subjunctive.

The perfect system comes from the third principal part

Fourth-conjugation deponents form perfect-system tenses with an agreeing participle plus forms of sum. The participle’s stem may be regular-looking (mentīt-, largīt-) or less transparent (expert-, ort-). English gives no clue which one Latin selects.

The participles agree: masculine mentītus, feminine experta, masculine ortus. Mentītus est can be translated “lied” or “has lied” according to context; the label “perfect” does not force English present perfect.

Imperatives and participles

The present imperative singular uses -īre, and the plural uses -īminī: mentīre! “lie!” and mentīminī! “lie!” to more than one person. Since ordering someone to lie is pragmatically unusual, the negative command is more useful:

Here mentīrī is the present infinitive after nōlī, while mentīre by itself would be a singular imperative. The difference between -īrī and -īre is meaningful.

Fourth-conjugation deponents also form present participles such as mentiēns “lying,” perfect participles such as mentītus “having lied,” and future participles such as mentītūrus “about to lie.” In (literary) and formal prose these participles allow dense clause compression; in straightforward teaching prose, an explicit subordinate clause may be easier to read.

Lexical variation is not free variation

Some fourth-conjugation verbs have unusual principal parts, mixed present-system forms, competing active forms, or meanings that shift across periods. Orior, for instance, has the fourth-conjugation infinitive orīrī but commonly uses third-conjugation forms such as oreris, oritur, and orimur beside regular fourth-conjugation formations elsewhere in its paradigm. Partior “divide” exists beside active partiō. These lexical facts do not authorize a learner to give every deponent a mixed or active paradigm. Similarly, later Latin may extend or regularize formations that a Classical composition exercise would avoid. Treat attested variants as properties of particular lexemes and registers, not as a productive switch.

Common Mistakes

1. Confusing third- and fourth-conjugation infinitives

2. Translating the ending instead of identifying the lexeme

3. Inventing a regular active perfect

4. Forgetting agreement in a deponent perfect

Key Takeaways

The present infinitive in -īrī identifies a fourth-conjugation deponent. Build its present system with fourth-conjugation passive-form endings, but interpret the subject as the agent or experiencer. For the perfect system, retrieve the third principal part and make the participle agree. Irregular stems such as expert- and ort- are exactly why principal parts, not English translations, organize the paradigm.