The infinitive form of a verb is usually preceded by "to"
(e.g., to run, to dance, to think). The word "to" is not a
preposition in this case; it is often called the "sign of the
infinitive". An infinitive can be used as a noun, an
adjective or
an adverb.
Examples:
To dance
was his ambition. (as a noun) His ambition
was to dance. (as a noun) They need
water to drink. (as an
adjective) The officer
returned to help. (as an adverb)
After certain verbs the "to" is dropped.
Examples:
I
helped her tidy the balcony. ("to"
dropped from "to tidy")
They
made him wait for a day. ("to"
dropped from "to wait")
Interactive example:
I am leaving at 5 o'clock to
raise the lobster pots before the storm.
[show me the infinitive form]