Functional Grammar

We define a word as noun or verb etc on the basis of its function in a sentence. That is, the same word can function as different parts of speech in different situations.

For example, there are a few words, that can function as nouns in some cases and verbs in other cases.

Love is life. (love - an abstract noun)
I love you. (love – a verb)

Where is your shop? (shop - an abstract noun)
I will shop on Monday. (shop – a verb)

Few of such words even differ in pronunciation when used as a verb.

Address (əˈdres, ऐड्रिस) - (address as an abstract noun)
Ex: May I have your address?

Address (a’dres, अड्रेस) - (to deliver a speech, working as a verb)
Ex: How do I address you?