ABSTRACT
Sentences are always finite, but clauses that form parts of sentences may be finite or non-finite. Finite declarative sub-clauses look exactly like declarative sentences in terms of structure, with the one exception that they can always have a complementiser. When it comes to form, there is one major sub-division of sub-clauses according to the form of the first verb of the verb string, namely, finite versus non-finite sub-clauses. Sentences are always finite, but clauses that form parts of sentences may be finite or non-finite. Clauses such as these are called non-restrictive relative clauses because the clause is there to restrict the reference of the noun itself. The fact that both types of clauses begin with the same element is no accident – they have developed from the same source, a type of development that is quite common cross-linguistically. When it comes to drawing trees representing the structure of sentences containing sub-clauses, there are two things that make it tricky.
