The infinitive is the most basic of the verb forms. Unlike the conjugated verb forms — the ones used most often in speech — an infinitive standing alone says nothing about how many people are performing the verb's action or when.
In Spanish, the infinitive is the verb form that appears in dictionaries. The infinitive always has one of three endings: -ar, -er or -ir. Standing alone, the infinitive is usually translated to English as "to" followed by the verb. For example, ver is usually translated as "to see," hablar as "to speak." But as we shall soon see, in sentences the Spanish infinitive can be translated a number of ways.
In this lesson, we look at instances where the infinitive functions as a noun. In other lessons linked to on this page, we look at the ways that infinitive functions with other verbs and prepositions, sometimes in ways that are unlike the use of the infinitive in English.
When used as a noun, the Spanish infinitive is always masculine and almost always singular. Like other nouns, it can be the subject of a sentence, a predicate nominative (usually a noun that follows a form of "to be" or ser) or the object of a verb or preposition. The infinitive noun sometimes retains the characteristics of a verb; it sometimes is modified by an adverb rather than an adjective and can sometimes have objects. It is often translated into the English gerund (the "-ing" form of the verb). Here are some examples of the infinitive being used as a noun:
As you may notice, the definite article el (or the contraction al) is not consistently used with the noun infinitive. It is most often used in certain set phrases and following some prepositions. When an infinitive is the subject of the sentence, the el is often optional; when it is used, it can give the sentence a more personal or informal sound.
Note also that the translations given above are not the only ones possible. http://spanish.about.com/od/infinitives/a/infinitive_noun.htm