The infinitive is the uninflected form of the verb such as to read, to write, to count, etc. Infinitives are divided into three categories: -ar, er, and -ir verbs. In addition to being the source of conjugated verbs, they also serve specific functions as parts of speech in their own right. They can be used in a causative construction, after verbs of sensory perception, after prepositions, as nouns, and as verbal objects.
If a speaker does not actually perform an action, but instead
causes something to happen, a causative construction can result.
Verbs such as mandar, hacer, and dejar typically
form part of the utterance.
Infinitives can follow verbs that imply a sensory perception,
such as sentir, percibir, ver, oír, oler,
etc.
After prepositions such as después de, antes de, para,
sin, etc. the infinitive follows, despite the -ing
ending in English.
The infinitive can be used as a noun, and it can function as a
subject or as an object. As in the previous use, care should be
taken not to allow the distraction of English usage, i.e. an
-ing ending.
Mirroring English syntax, many verbs precede the infinitive,
which acts as an object of the verb.