There is a lot of discussion about simple, compound and complex sentences. However, I find this difficult to apply to verbs that project e.g. mental verbs "think, believe, understand" etc and verbal verbs "say, claim, state" etc.
"He said ok" - this is simple because it only has one clause (one main verb).
"He said that he was ok" - although this has two verbs and may be called a complex sentence, the clause "that he was ok" functions as the object of the verb. It answers the question "what did he say" - "he said X" where x = "that he was ok". From the perspective of meaning, can it be argued that this is a simple clause with an embedded clause functioning as object? Therefore, from a functional perspective, there is only one simple clause. Opinions?