fellow grammarians.

When it comes to a clause, we'd naturally understand that each of them has a lexical class to it, and, the part of speech they serve as in a sentence.

Adjective + that clause has never been a rare usage. It's rather easy to get right the that clause in sentence 'It's important that this will be done' for example. The 'it' here is a formal subject, hence the that clause being the true subject. And the lexical class of this that clause is noun. Therefore, it is both a subject clause, and a noun clause.

But in the case of 'I'm sure + that clause', this gets me confused. 'I am sure' being a complete sentence which ends with a predicative, I don't know what the that clause after the predicative 'sure' serves to be in terms of part of speech. Sure, it should be a noun clause as always, but, what part of speech is it?

Thanks in advance!

  • 1
    You are not identifying noun clauses correctly yet; the that-clause after "sure" is not at all a noun clause. Here is a link giving explanations:wikihow.com/Identify-a-Noun-Clause . The gist of it is this: "Simply put, a noun clause is a dependent clause that takes the place of a noun in the sentence. […] If a dependent clause can stand in for a person, place, or thing, then it’s a noun clause." If you replace it by a noun and the resulting sentence makes sense, then you have a noun clause. For instance "I'm sure people." makes no sense at all.
    – LPH
    Apr 10, 2021 at 9:56
  • 3
    @LPH. Traditional grammar does classify the that clauses in the OP's examples as noun clauses. But the term 'noun clause' is a misnomer, particularly as many of the so-called 'noun clauses' cannot be replaced by nouns, as the OP's examples demonstrate. The OP's examples are best classified as declarative content clauses (the default kind of finite subordinate clause) functioning as complement of the adjectives "important" / "sure". There is nothing at all to be gained by calling them 'noun clauses'
    – BillJ
    Apr 10, 2021 at 11:20
  • @BillJ "That" clauses, when adjectival complements are, as you say, classified as nominal clauses, but in this case a noun phrase does not fit in; what is needed is a prepositional phrase. The question is not one of "gaining" something but of describing truly what is the nature of the grammatical element considered. Does it fulfill the functions of a noun or not? It seems that it does: subject, object; only nouns (NP) can have those functions. So, I believe that grammar does classify judiciously this element as being of the nature of the noun (there might be difficulties as here, though).
    – LPH
    Apr 10, 2021 at 12:08
  • @LPH Why? It doesn't matter whether or not the clause can be replaced by a noun -- trad grammar still calls it a 'noun clause'. But modern grammar does not use the term 'noun clause' -- it's meaningless. Finite subordinate clauses are not noun clauses under any circumstances. They have their own classifications, i.e. content, comparative and relative. The first two almost always function as complements, while the relatives are modifiers. There is nothing to be gained by calling content clauses 'noun clauses'. Why would anyone want to?
    – BillJ
    Apr 10, 2021 at 12:18
  • @BillJ It is a useful nomenclature because it describes a category of clauses that definitely have in common a precise syntactical characteristic that sets them apart from other clauses, no more than that, except for the fact that it is simply true.
    – LPH
    Apr 10, 2021 at 12:52

1 Answer 1


[1] It's important [that this is done].

[2] I'm sure [that this will be done].

The lexical class of the bracketed elements is 'declarative content clause'.

In [2] The subordinate clauses combines with the adjective it complements to form a larger adjective phrases functioning as predicative complement of "be". By contrast, in [1] (an extraposed construction) the predicative complement is just "important", just as it is in the basic, non-extraposed, version (see below).

I would strongly recommend dropping the term 'noun clause'. The classification of finite subordinate clauses is based on their internal form rather than spurious analogies with the parts of speech.

Note that in the extrapostion constuction in [1], the subject is the dummy pronoun "it". The that clause is an extraposed subject, but that doesn't mean it's a kind of subject -- it's an element in extraposed position, outside the verb phrase corresponding to the subject of the basic version:

[That this is done] is important.

  • "That this is done" does not have the function of adjective complement; its function is called "real subject", whereas you call the subject "it" an artificial subject or dummy subject (dictionary.cambridge.org/grammar/british-grammar/dummy-subjects). Same thing in "It's important to do this.".
    – LPH
    Apr 10, 2021 at 12:41
  • This analysis makes of "that this is done" the complement of its own predicative complement; that is not possible.
    – LPH
    Apr 10, 2021 at 12:57
  • The Cambridge reference I provide uses the term "real subject"; that is not ESL. //If you have a subject it is the subject of some verb and you can't have "That this is done is."; this again is nonsense.
    – LPH
    Apr 10, 2021 at 13:11
  • @LPH "That this is done" in [1] is not called a 'real subject' but an extraposed subject, as I said in my answer. It's only the subject in the non-extraposed version, as shown in my answer.. The grammatical subject of [1] is the dummy pronoun "it". In [2] "that this will be done" is complement of "sure", with which it combines to form the larger PC "sure that this will be done"
    – BillJ
    Apr 10, 2021 at 13:12
  • 1
    @LPH What remains a subject? No grammarian would say that "that this is done" is the grammatical subject of [1]. That would be a ridiculous mistake. We know that "it" is the subject because it inverts with the verb to form an interrogative: "Is it important that this is done?" The PC in [1] is just "important", just as it is in the non-extraposed version.
    – BillJ
    Apr 10, 2021 at 13:18

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