Locate the infinitive. Since it is used as a noun, determine its noun use.

Her ambition is to swim gracefully.

Infinitive:

Use:

Infinitive: 'To swim.'

The use: Verb

Explanation:

Infinitive is a verb that comes after 'to' in a sentense. For example, she came to beg for representation in the congress.

In the above sentense, the infinitive is used as a verb, that is, it is used to show her action of swimming.

The infinitive can be located in a random part in the sentense to act as a noun, an adjective or a verb, depending on the nature of the sentense.

Infinitive: to swim

Use: noun predicate or predicate nominative

Explanation:

The infinitive is the basic form of a verb, that is, a form with no inflections - no changes due to a relationship with a subject. It usually comes preceded by "to".

In the sentence "Her ambition is to swim gracefully", the infinitive is "to swim". It functions as a noun would and, in this particular sentence, it is a predicate nominative. A predicate noun or predicate nominative is a noun or noun phrase that comes after a liking verb (such as "to be") and has the purpose of providing further information about the subject of the sentence. Predicate nouns do not follow action verbs, since they don't express actions, but states of being. "To swim" is providing further information about "her ambition".