1）他說的那句話。
In example (1), ‘他說的’ is a part of a Noun phrase. The head noun of the noun phrase is a modified noun.
2）那句話是他說的。
In example (2), ‘他說的’ is a part of a Predicate. The head noun of the noun phrase is a topicalized noun.
In sum, the construction of [X-de] N can be formed as follows, which is presumed to be true or given.
[Modifier / Relative clause / Cleft-clause] DE
