Queo and Nequeo

The defective verbs queō, quīre, quīvī (or quiī), quitum “be able” and nequeō, nequīre, nequīvī (or nequiī), nequitum “be unable” are inflected largely on the pattern of eō “go.” Their usual complement is a present infinitive: hoc facere nequeō “I cannot do this.” That morphological resemblance does not give them a motion meaning in Classical usage: they are modal verbs.

Possum is the ordinary all-purpose verb for “can.” Queō is much less common and often occurs with nōn; nequeō is better established, especially when inability is emphasized. Both occur in (neutral Classical) prose, but they are conspicuous in comedy and poetry (literary). Because their paradigms are incomplete and unevenly attested, learners should recognize more forms than they actively produce.

The core present forms

The present indicative is conventionally laid out beside eō because it shows a comparable alternation between ī- and e- forms.

Review The Present Indicative of eō if the alternation between ī- and e- is unfamiliar. Queō and nequeō inherit that alternation but preserve only part of the full paradigm.

The alternation between quī- and que- parallels īs beside eunt in eō. It is lexical morphology, not a choice governed by meaning. Learn the six forms as a set rather than trying to attach ordinary fourth-conjugation endings.

The table shows the traditional citation paradigm, not six equally secure choices for Classical prose. In particular, positive second-person plural quītis is supported only by post-Classical evidence, and nequītis is likewise a poor production form. Use potestis or nōn potestis when an ordinary Classical second-person plural is needed.

Infinitival complements and subject control

Like possum, these verbs normally share their subject with the infinitive. In puella currere nequit, the girl is both unable and the understood runner. Latin does not insert an English-style “to” word; currere itself is the infinitive.

A passive infinitive is possible when what cannot happen is passive: iānua aperīrī nequit “the door cannot be opened.” The modal remains active and third-person singular because nominative iānua is its subject. A few passive forms of queō/nequeō occur outside ordinary Classical prose, especially with passive infinitives, but they are (archaic or later) and not a productive Classical pattern.

English speakers sometimes try to make the modal itself passive because the English translation contains “be.” Latin instead places the passive morphology on aperīrī.

Imperfect, future, and subjunctive

The surviving imperfect is patchy. Securely attested cells include quībam, quībat and nequībat, nequībant in the indicative, and quīret, quīrent and nequīrem, nequīret, nequīrent in the subjunctive. Present subjunctive evidence supports queam, queās, queat, queāmus, queant and the corresponding nequeam, nequeās, nequeat, nequeāmus, nequeant; a second-person plural is not securely attested. Some reference tables fill the gaps by analogy, but a defective verb's possible-looking cell is not thereby Classical.

Future forms such as quībō and quībunt are attested, chiefly in early or later sources rather than ordinary Classical prose. In active composition, (neutral Classical) poterō is normally the safer future “I shall be able.” That is not because quībō is mechanically impossible; it reflects the defective verb's patchy historical usage.

Perfect-system forms

The perfect is built like the perfect of eō: quīvī or shorter quiī, and nequīvī or nequiī. Here too the actual inventory, not a mechanically completed paradigm, controls usage. Attested positive cells include quīvī, quīvit, quīvērunt, perfect subjunctive quīverit and quierint, pluperfect subjunctive quīvissent, and perfect infinitive quīsse. The better represented negative side includes nequīvī, nequīstī, nequīvit, nequīvērunt, selected perfect-subjunctive forms, third-person pluperfect nequīverat/nequīverant, and perfect infinitive nequīvisse or nequīsse. Do not infer missing persons merely because their endings would be predictable.

These perfects report completed occasions of ability or failure. Do not translate nequīvī by its morphology alone as an English present perfect; context may require “I could not” or “I was unable.” Latin perfect aspect and English tense phrasing do not align one for one.

Queō, nōn queō, nequeō, and possum

Queō and possum overlap, but they are not identical in distribution. Possum has a robust, complete paradigm and is the default in all registers. Positive queō is comparatively limited. Negative nōn queō and lexical nequeō are more frequent; nequeō can make inability feel like a single, emphatic predicate.

There is no productive semantic rule by which every instance of possum can be replaced with queō. Treat the choice as lexical and register-sensitive.

A parsing checklist

For nequeunt fugere, identify -unt as third-person plural, recognize the neque- allomorph, and take fugere as its infinitival complement. The result is present indicative active, third-person plural: “they cannot flee.” Do not start from English “cannot,” which hides person, number, and the separate infinitive.

For queat, identify third-person singular present subjunctive and then find the trigger: purpose, result, relative characteristic, potential meaning, or another subjunctive environment. The form itself does not mean English “might” in every context.

Common Mistakes

1. Conjugating queō as a regular fourth-conjugation verb

2. Conjugating the dependent infinitive for person

3. Inventing passive modal forms in ordinary prose

4. Treating the perfect as present time

5. Filling a rare future cell without regard to usage

Key Takeaways

Queō and nequeō are defective modal verbs inflected largely on the pattern of eō. Their central Classical forms include present queō/quīs/quit/quīmus/queunt and the corresponding nequeō forms, selected subjunctives such as queam/nequeam, attested imperfect cells such as quībat/nequībat, and perfect quīvī/nequīvī. They govern an infinitive, remain active in ordinary Classical prose, and must be learned from attestation rather than completed by analogy.