Very common mistake many foreign learners make. When they see the words “am, is, are” , the translations come out as 我是累， or 她是忙etc.
Though, in the English sentence such as “ I am tired”, “am” does not contribute real meanings to its sentence, instead, together with “tired” to function as predicate. Since “am” has no affirmative meaning, one should not force to give its meanings when think of the sentence in Mandarin Chinese.
Instead being far-fetched to put “是” in the sentence, we should say “我(很)累”. “累” is an adjective; unlike English it can work as the predicate to have the same function of verbs.
“很” is an adverbial Which originally means “very” and usually modifies adjectives. Though in mandarin, when there’s the time the predicate is formed by an adjective instead of verb we usually will add the adverbial “很” to make the sentence sound complete, in this case “很” nearly lost its original meaning of “very” or its original meaning became very weak, only to be there as part of a finished sentence.
So instead of saying “我累” which grammar wise is not wrong, “我很累” is more of a correct way of saying it.
Apply the same rule to the situations whereas the predicate is an adjective instead of verb.
Look at the sentences below, and say them in Mandarin:
He is tall.
She is pretty.
I am disappointed.
The little boy is happy.