What are clauses?
There are two main factors ‘head’ and ‘the complements’ in the sentences as I reviewed before. For the complements, we can use not only phrases but also clauses. Then, what are clauses? Clauses have a formation of sentence and look like a sentence. However, compared to sentences, clauses cannot stand by themselves, and they should be included within a whole sentence.
In this sentence above, the TP [John thinks that Mary is smart] is a sentence. On the other hand, the CP (that Mary is smart) is not a sentence, but a clause.
First, I’ll deal with That Clauses. This clause is composed of two kinds, finite clause and bare-stem clause. The finite clauses are followed after epistemic verbs or say-type verbs, whereas the bare-stem clauses are formed only when it is influenced by external syntax. I already showed one kind of finite clauses above, so I’m going to introduce bare-stem clause here.