Third-iō Conjugation Paradigm
The third-iō conjugation is the awkward middle child: a small set of third-conjugation verbs whose stems carry an extra -i- that surfaces in some forms and disappears in others.
The headliner is capiō, capere, cēpī, captum ("take, capture"). The infinitive capere is short, plain third-conjugation; but the present says capiō (not capō), the third plural says capiunt (not capunt), and the future is capiam, capiēs — built like audiam from the fourth.
That split is the trap. Capit looks exactly like regit ("he rules"), so you can't tell third from third-iō by sight. You have to know the verb.
Roughly fifteen common verbs do this — capiō, faciō, fugiō, iaciō, rapiō, cupiō, plus high-frequency compounds like accipiō, conficiō, interficiō, recipiō — and they cover so much of Caesar that learning the family pays off fast.
Third-conjugation infinitive, but the present-stem -i- surfaces in the 1st sg., 3rd pl., and the entire future and imperfect.
About fifteen verbs do this — memorize capiō, faciō, fugiō, iaciō, rapiō, cupiō plus the -cipiō / -ficiō compounds, and you've got them all.
| Case | Singular | Plural |
|---|---|---|
| Pres. 1 | capi-ō | cap-imus |
| Pres. 2 | cap-is | cap-itis |
| Pres. 3 | cap-it | capi-unt |
| Impf. 1 | capi-ēbam | capi-ēbāmus |
| Impf. 2 | capi-ēbās | capi-ēbātis |
| Impf. 3 | capi-ēbat | capi-ēbant |
| Fut. 1 | capi-am | capi-ēmus |
| Fut. 2 | capi-ēs | capi-ētis |
| Fut. 3 | capi-et | capi-ent |
| Perf. 1 | cēp-ī | cēp-imus |
| Perf. 2 | cēp-istī | cēp-istis |
| Perf. 3 | cēp-it | cēp-ērunt |
| Plup. 1 | cēp-eram | cēp-erāmus |
| Plup. 3 | cēp-erat | cēp-erant |
| Fut. Perf. 1 | cēp-erō | cēp-erimus |
| Fut. Perf. 3 | cēp-erit | cēp-erint |
| Case | Singular | Plural |
|---|---|---|
| Pres. 1 | capi-am | capi-āmus |
| Pres. 2 | capi-ās | capi-ātis |
| Pres. 3 | capi-at | capi-ant |
| Impf. 1 | cap-erem | cap-erēmus |
| Impf. 3 | cap-eret | cap-erent |
| Perf. 1 | cēp-erim | cēp-erīmus |
| Perf. 3 | cēp-erit | cēp-erint |
| Plup. 1 | cēp-issem | cēp-issēmus |
| Plup. 3 | cēp-isset | cēp-issent |
| Case | Active | Passive |
|---|---|---|
| Imper. Pres. Sg. | cape | capere |
| Imper. Pres. Pl. | capite | capiminī |
| Imper. Fut. Sg. | capitō | capitor |
| Imper. Fut. Pl. | capitōte | — |
| Infin. Pres. | capere | capī |
| Infin. Perf. | cēpisse | captus esse |
| Infin. Fut. | captūrus esse | captum īrī |
| Partic. Pres. | capiēns, -ientis | — |
| Partic. Perf. | — | captus, -a, -um |
| Partic. Fut. | captūrus, -a, -um | — |
| Gerund | capiendī, -dō, -dum, -dō | — |
| Gerundive | — | capiendus, -a, -um |
| Supine | captum, captū | — |
See It In Action
— Verg. Aen. v. 185
The 3rd-singular capit is where third-iō hides — drop the -i-, looks exactly like a plain third-conjugation form. Only the dictionary entry tells you which family it belongs to.
— Verg. Aen. v. 315
Capiunt is the giveaway form: any third-conj. verb ending in -iunt (not -unt) is third-iō. Compare regunt "they rule" vs capiunt "they take."
— B. G. v. 37. 6
Interficiō ("kill") is inter- + faciō, so it inherits the third-iō pattern. The -iunt ending tells you instantly it's not regular third.
— B. G. vii. 90. 1
Two third-iō verbs in seven words — cōnficiō in the ablative absolute cōnfectīs and recipiō in the main verb recipit. Caesar's narrative voice runs on this family.
In the singular present, third-iō verbs lose their -i- and look identical to plain third. The give-aways are -iō (1sg), -iunt (3pl), and the entire future.
stem keeps -i- in 1sg, 3pl, and future
capit / capiunt / capiet
he takes / they take / he will take
no -i- anywhere in present system
regit / regunt / reget
he rules / they rule / he will rule
Tip: Ask: does the 3rd-plural end in -iunt or -unt? -iunt means third-iō. Also: is the future 1sg -iam (third-iō / fourth) or -am (plain third)? Capiam vs. regam settles it instantly.
Caesar writes cīvitātem recipit. What conjugation is recipit, and how can you tell?
Study Tips
- •Memorize the capiō present indicative as your anchor — the -iō / -is / -it / -imus / -itis / -iunt pattern is the whole shape of the conjugation in one row.
- •Whenever you see a verb with a -iō first principal part and a short -ere infinitive (not -īre, not -ēre), tag it third-iō and expect the -i- to come back in the future and in -iunt.
- •Drill the high-frequency compounds (accipiō, conficiō, interficiō, recipiō) as their own list — Caesar uses them constantly, and recognizing them on sight saves seconds per sentence.
- •When parsing a 3rd-singular like capit or facit, don't try to tell third from third-iō from the form alone — check the dictionary entry once, then commit it to memory.