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Work Unit Twenty-One: Quiero ser rico
Uses of the Infinitive
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By now you've probably learned that the basic form of the verb is known as the infinitive, and it is the verb form that ends in -ar, -er or -ir. In this lesson you will learn a number of ways you can use the infinitive and thus vastly expand the circumstances in which you can use them.


Complete the lesson on pages 225-32 of the textbook. To hear how the days of the month are pronounced, please listen to the audio lesson, which also gives some more information on the rules for conjugating irregular verbs.

Be sure to complete the exercises. Although copyright rules and fairness to other students using this book prevent me from publishing all the answers, you can check the answer page to see an answer to the first question in each section to help get you started. If you have any questions, feel free to ask them on the bulletin board.


You may not have thought it much before reading this lesson, but we use the infinitive form of verbs quite often in English. In English the form is represented by "to" followed by the verb form. Thus "to go," "to eat," and "to swim" are all English infinitives. In Spanish, the infinitive is the basic, unconjugated form of the verb, always ending in -ar, -er or -ir.

This lesson focuses on the complementary infinitive, cases where the infinitive gramatically fulfills a function similar to the object of a preposition or verb. You should read the examples in the book carefully, as they cover the most common ways in which infinitives are used. However, infinitives can also be used in other ways, often functioning as a noun. When used as nouns, infinitives take masculine adjectives and articles. Usually, infinitives are translated as English infinitives; however, sometimes they are translated as conjugated verbs in English or as the "-ing" form of verbs.

The following chart shows some of the different ways, including those explained in the text, in which infinitives are used in Spanish. Although you don't at this point need to learn all the ways, it is helpful to be able to familiarize yourself with them to help you when you're reading or conversing in Spanish. Thist list isn't exhaustive, but it covers the uses you're most likely to come across.

as the subect of a sentence El leer es importante. Reading is important (or, to read is important). Note: Infinitives when used as nouns are masculine; use of el or la preceding the infinitive is often optional.)
after verbs of obligation Debo salir a casa. I ought to leave for home.
after verbs of desire or intent Quisiera viajar a la casa de mi madre. I would like to travel to my mother's house. 
after verbs indicating ability No puedo nadar. I can't swim (or, I am unable to swim.).
after tener que ("to have to") or hay que ("it is necessary to"). Tiene que trabajar mucho. She has to work much. Hay que comer. It is necessary to eat.
after a verb of motion followed by a Voy a comprar una bicicleta. I am going to buy a bicycle. Vino aquí a comer. He came here to eat.
after verbs of the senses Te oí hablar. I heard you talking. ¿Me viste nadar? Did you see me swimming?
as the object of de Tengo miedo de volar. I am afraid of flying (or, I am afraid to fly).
as the object of para Vivimos para comer. We live to eat.
as the object of por Vivimos por comer. We live by eating.
as the object of sin Habla sin pensar. He speaks without thinking.
after al in the sense of "upon" to indicate vague causality Al ver la casa, lloró. Upon seeing the house, he cried.
in impersonal commands of prohibition No fumar. No smoking.

Coming up

In the next lesson we'll learm study another part of speech that can serve as the object of a preposition — pronouns.

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