In English, the copular verb 'is' is used to link the subject to the predicate. For example in the sentence: The girl is smart, the copular verb 'is' is required to indicate that the adjective 'smart' is a description of the subject 'the girl'. In Mandarin, the copular verb is not required in this situation. The sentence 这个女孩聪明 places the subject and predicate next to each other without the need of the verb 是.It is common to add an adverb or adjective between the subject and predicate, for example 很, 太, 真, but the verb is not required.