Infinitive Phrases — I can translate infinitive phrases used with verbs of wanting/being able at my level.

Historical Context & Motivation

Latin authors did not simply express ideas one verb at a time. From the earliest Roman literature, writers needed a way to convey complex intentions — what a character wanted to do, what they were able to do, or what they decided to do. The complementary infinitive construction became one of the most natural and frequent tools in the Latin language for expressing these layered ideas. Understanding this construction opens a doorway into reading real Latin prose and poetry with confidence.

The central question this lesson addresses is straightforward but essential: when a Latin sentence includes a verb of wanting, being able, or deciding, how do you recognize the infinitive that completes it, and how do you translate the whole phrase into smooth English? Once you can answer that question, you unlock a huge portion of the Latin sentences you will encounter.

Core Principles & Definitions

Before diving into examples, let's establish the foundational ideas you need. A complementary infinitive is an infinitive that completes the meaning of another verb. The word 'complementary' comes from the Latin complēre ('to fill up, to complete'). Without the infinitive, the main verb's meaning feels incomplete — you can't just say 'I want' without telling the reader what you want to do.

Visual Explanation — Sentence Architecture

The diagram below maps out the internal structure of a Latin sentence that uses a complementary infinitive. Notice how the head verb sits at the core of the sentence while the infinitive phrase branches off to complete its meaning. Any direct objects or modifiers attach to the infinitive, not to the head verb.

Notice in the diagram that the direct object puellās is in the accusative case because it receives the action of the infinitive vidēre, not the action of potest. This is a common source of confusion, so keep in mind that the infinitive can carry its own objects, adverbs, and prepositional phrases — everything that a regular verb can carry, except a separate subject.

How It Works — The Grammar Mechanics

Latin does not have a single word for 'can' or a simple auxiliary verb system like English does. Instead, it uses a fully conjugated verb — possum, posse, potuī — paired with a complementary infinitive. Similarly, verbs of wanting (volō, velle, voluī) and their relatives require an infinitive to express what is desired. Let's examine the main head verbs and the patterns they create.

The Key Head Verbs

The Translation Formula

Detailed Breakdown — Possum & Volō in Action

The two most common head verbs you will encounter are possum (ability) and volō (wanting). Both are irregular, so their conjugations require memorization. The diagram below presents the present-tense forms of each verb side by side, showing how each pairs with an infinitive.

A crucial observation from the chart is that the infinitive remains in its dictionary form no matter what the subject is. Whether you say possum vidēre or possunt vidēre, the infinitive vidēre does not change. All the grammatical information about the subject — person, number — is carried by the head verb alone. This is exactly how English works too: 'I can see,' 'they can see' — the infinitive 'see' stays constant.

Worked Example — Translating Step by Step

Let's work through a complete sentence from start to finish, applying the principles we have covered. The sentence is: Mīlitēs castra mūnīre nōn poterant.

Complementary Infinitive vs. Indirect Statement

One of the trickiest parts of Latin grammar is telling the complementary infinitive apart from the indirect statement. Both constructions use infinitives, but they work in very different ways. The table below highlights the key differences so you can diagnose which construction you are facing in any given sentence.

Connection to Advanced Constructions

Mastering the complementary infinitive now prepares you for several more complex constructions you will encounter in Latin 3 and beyond. The same head verbs that take complementary infinitives can also appear with subjunctive clauses, and the differences between these approaches become a rich area of study in advanced Latin. Below is a preview of how this concept connects to what lies ahead.

You may also notice that many of these head verbs appear in the subjunctive mood themselves when embedded in purpose clauses or result clauses. For instance, a sentence like Tam fortis erat ut vincere posset ('He was so brave that he was able to conquer') puts posset in the subjunctive, but vincere is still a complementary infinitive. The foundational pattern you are learning now will remain the same no matter how complex the surrounding grammar becomes.

Practice Problems

Lesson Summary