By now you know that the basic, non-conjugated form of a Spanish verb is called an "infinitive." You've probably already spent a good deal of time learning how to conjugate infinitives or change them so that they agree with their subjects. But we don't always conjugate our infinitives. There is a wide variety of non-verb situations in which we leave the infinitive unchanged.
But first of all, a quick reminder. Any verb that has a subject must be conjugated:
Yo leo el periódico.
Yo leer el periódico.
I read the newspaper.
That's enough on conjugating. When can we leave our infinitives unconjugated?
Using Infinitives as Subjects
Note: Sometimes the article el is used with an infinitive to emphasize the fact that it is a subject.
When we want to use a verb as a noun in English, we use gerund ("-ing") form of the verb. We do not do this in Spanish. Instead of a gerund, we just use the infinitive. Resist the urge to use the present participle ("-ando" or "-iendo") form of the verb:
Jugar básquetbol es muy divertido.
Playing basketball is very fun.
El leer es interesante.
Reading is interesting.
It may not look like it since they come later in the sentence, but infinitives used with verbs like gustar are actually subjects too:
Me gusta nadar y patinar sobre hielo.
I like to swim and ice skate. / Swimming and ice skating are pleasing to me.
A ella le fascina cocinar.
Cooking fascinates her.
Using Infinitives as Objects of a Verb
Note: It's possible to string together many infinitives: Me gustaría poder saber apreciar el arte.
What's an "object of a verb"? It's a fancy way of describing an infinitive that comes immediately after a conjugated verb. Deber (to should), poder (to be able to), querer (to want to), and soler (to usually) are verbs which are commonly followed by an infinitive. They are sometimes referred to as "modal verbs." Modal verbs need to be followed by another verb because they don't make much sense on their own. Some examples:
Debes pagar la multa.
You should pay the fine.
¿Puedo ir al baño?
Can I go to the bathroom?
¿Quieres bailar conmigo?
Do you want to dance with me?
Suele mirar televisión después de las clases.
He usually watches television after school.
Other verbs that are often followed by infinitives are decidir (to decide to), esperar (to hope to), intentar (to try to), preferir (to prefer to), and saber (to know how to). Some examples:
Decidí regresar inmediatamente.
I decided to return immediately.
Ella espera viajar a Londres.
She hopes to travel to London.
Preferimos no tener tarea.
We prefer not to have homework.
Intentamos mover la piedra.
We tried to move the stone.
Yo sé nadar muy bien.
I know how to swim very well.
Using Infinitives with Sensory Verbs
Note: The infinitive must immediately follow the sensory verb.
Infinitives can also be used directly after sensory verbs:
Escucho hablar el poeta.
I listen to the poet speak.
La ví bailar.
I saw her dancing.
Siento calentar el sartén.
I feel the frying pan heating up.
Huelo cocinar la sopa.
I smell the soup cooking.
Using Infinitives as Objects of a Preposition
Note: When used with an infinitive, al means "upon."
When following a preposition, verbs should be left in the infinitive. Again, resist the urge to use the present participle like we do in English:
Al llegar entendí el problema.
Upon arriving I understood the problem.
Siempre come antes de estudiar.
He always eats before studying.
Ella salió después de practicar.
She left after practicing.
Ten cuidado en revisar tu informe.
Be careful in revising your report.
Note: When used with an infinitive, para means "in order to."
The words por and para are also prepostions are used with infinitives. Some examples:
Toma apuntes para entender mejor.
She takes notes in order to understand better.
¡Gracias por ayudarnos!
Thanks for helping us!
The rules for using por and para are long and complex. Read more about them at Using Por and Para.
Using Infinitives in Special Expressions
There are many special infinitive constructions in Spanish that use a bewildering variety of prepositions (like a, de, en, and con). Some of them are somewhat logical. Others make no sense whatsoever. You'll be much better off just memorizing which verbs go in which category than trying to figure out why.
The first category:
Verb + a + Infinitive
Note: When used with an infinitive, volver a means "to do something again."
Why do we need to put an a before some infinitives? We just do. Verbs commonly appearing in this category are aprender, ayudar, comenzar, empezar, enseñar, ir, and volver. Some examples:
Aprendí a esquiar.
I learned to ski.
Ella empezó a llorar.
She began to cry.
Mi maestro me enseñó a hablar español.
My teacher taught me to speak Spanish.
Voy a ir al partido mañana.
I'm going to go to the game tomorrow.
Él volvió a leer el poema.
He read the poem again.
You may occasionally hear expressions like "a ver" or "a leer" meaning "let's see" or "let's read." All that's happening here is that "ir + a + infinitive" expression has been shortened by removing the vamos.
The next category on the list:
Verb + de + Infinitive
Note: When used with an infinitive, acabar de means "to just have done something."
Why do we need to put a de before some infinitives? We just do. Verbs that fall into this category are acabar, dejar, tratar, tratarse. Some examples:
¡Pero acabo de llegar!
But I just arrived! / But I just got here!
Mateo dejó de leer.
Mateo stopped reading.
Juana, trata de ser más amable.
Juana, try to be nicer.
La película se trata de correr en los juegos olímpicos.
The movie is about running in the Olympic Games.
Verb + en + Infinitive
Insistir and pensar are the main verbs in this category. Some examples:
¡Ella insiste en pintar!
She insists on painting!
Pienso en estudiar la ley.
I'm thinking about studying law.
This is followed by the strangest category yet:
Verb + con + Infinitive
Acabar, bastar, contar, and soñar
are the verbs to worry about in this category. Some examples:
No me basta con estudiar quince
It's not enough for me to study fifteen minutes.
Pues, cuenta con estar aburrido.
Well, count on being bored.
Sueño con viajar a una playa
I dream about traveling to a Caribbean beach.
As you can see this is a weird category
because the word con, which is usually translated "with,"
inexplicably becomes "to," "on," and "about."
And the last category:
Verb + que + Infinitive
Note: When used with an infinitive, both tener que and haber que mean "to have to" or "to be necessary to."
The verbs to remember here are tener and haber. Some examples:
¡Tienes que seguir las reglas!
You have to follow the rules!
Hay que estudiar.
It's necessary to study. / You've got to study.
Using Infinitives as Impersonal Commands
You should conjugate your commands according to the subject (the person you're commanding). But that's not always possible. For example, if you hang a sign in a store with a command on it, you have no idea who is going to be reading it. Because of this, non-conjugated infinitives are often published as impersonal commands:
No echar basura
After learning the subjunctive you may be tempted to overuse it. Remember, if the subject doesn't change from one clause to the next, use an infinitive, not a subjunctive verb:
Yo quiero visitar Machu Picchu.
Yo quiero que yo visite Machu Picchu.
I want to visit Machu Picchu.