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Imperator certus est milites in oppido vigilare.

Imperator certus est milites in oppido vigilare.
The emperor is sure that the soldiers are keeping watch in the town.
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Questions & Answers about Imperator certus est milites in oppido vigilare.

Why is milites in the accusative plural?

Because milites is the subject of an indirect statement (an accusative + infinitive construction). In Latin, when a verb of knowing, thinking, perceiving, being sure, etc. introduces a reported fact, Latin often uses:

  • accusative for the logical subject (milites)
  • infinitive for the verb (vigilare)

So milites vigilare = that the soldiers are keeping watch.

What kind of construction is milites in oppido vigilare?

It’s an indirect statement (also called accusative and infinitive or AcI):

  • milites = accusative “subject” of the clause
  • vigilare = infinitive “verb” of the clause
  • in oppido = prepositional phrase modifying vigilare

This whole unit is what the emperor is certain about.

Why does Latin use an infinitive vigilare instead of a finite verb like vigilant?

In English we often use that + finite verb (that the soldiers are keeping watch). Latin commonly expresses the same idea with accusative + infinitive after verbs/adjectives of knowing, saying, thinking, etc.
So instead of certus est quod milites vigilant (less standard), Latin prefers certus est milites vigilare.

How do I know what tense vigilare is, and what time it refers to?

Vigilare is a present active infinitive. In indirect statement, the infinitive’s tense is usually relative to the main verb:

  • present infinitive = action contemporary with the main verb

So if certus est is present (“is certain”), then milites vigilare means “the soldiers are keeping watch” (at the same time).

What does certus est literally mean, and how does it work grammatically?

Literally, certus est means he is sure/certain (more literally: “he is settled/decided”).
Grammatically, certus is an adjective agreeing with imperator (nominative masculine singular), and est is the linking verb. The thing he is sure of is then expressed by the AcI: milites … vigilare.

Could Latin also say Imperator certus est milites in oppido vigilare with de + ablative instead?

With certus, Latin commonly uses either:

  • certus est + infinitive (as here), or
  • certus est + de + ablative when you mean “certain about something” as a topic, not a full statement.

But de + ablative would not naturally replace the full idea “that the soldiers are keeping watch.” It would shift meaning toward “certain about the soldiers / about the town,” etc., rather than expressing the complete proposition.

Why is in oppido ablative? How do I tell?

The preposition in can take:

  • ablative = location (in the town)
  • accusative = motion into (into the town)

Here it’s in oppido (ablative singular), so it means in the town (where the soldiers are keeping watch), not “into the town.”

Does in oppido describe the emperor or the soldiers?

It naturally modifies vigilare (the action of keeping watch), so it describes where the soldiers are keeping watch: in oppido.
Nothing in the sentence suggests the emperor is in the town.

Is the word order important here? Could it be rearranged?

Latin word order is flexible. The core relationships are shown by endings:

  • Imperator (nom.) = subject of est
  • milites (acc.) = subject of vigilare (in indirect statement)

You could see variants like:

  • Imperator certus est vigilare milites in oppido.
  • Certus est imperator milites in oppido vigilare.

The given order is straightforward: main clause first, then the indirect statement.

Could certus ever take a genitive or another case like some adjectives do?

Some adjectives do govern specific cases, but certus most commonly appears with:

  • an infinitive clause (certus est + infinitive) or
  • de + ablative (“certain about…”)

You may also see certior in expressions like certiorem facere (“to inform”), but that’s a different pattern.

Why is Imperator nominative if English might say “The emperor is certain that…”?

Because Imperator is simply the subject of the main verb est:

  • Imperator certus est = “The emperor is certain.”

Then the “that…” part is expressed by an indirect statement (milites … vigilare), not by changing the case of imperator.

What exactly does vigilare mean here—“to be awake” or “to stand guard”?
Vigilare can mean “to be awake,” but in military contexts it often means to keep watch / stand guard. With milites and a location (in oppido), the “standing guard” sense is the natural one.