In the phrase:

He demonstrated that he was true

  1. What word class does that belong to?

  2. In general, which word classes can it belong to? For example, relative pronoun, determiner, ...


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It is a complementiser, or subordinator. You could call it a kind of conjunction if you like.

"That" can also be a demonstrative pronoun or determiner. It sometimes also appears to be a relative pronoun (similar to "which"), but there is a preferable analysis where it is a complementiser and there is a suppressed "which".

Edit: correct "adjective" to "determiner".

  • Thank you very much. Can you give me an example with "that" functioning as an adjective? – LISA Nov 30 '15 at 18:11
  • No, I can't, because it isn't (though I think it used to be analysed that way). I mean "determiner", and have edited my answer. Thank you. – Colin Fine Nov 30 '15 at 18:13
  • @LISA When I learned grammar (around the time Grendl was a pup), sentences were analyzed in terms of parts of speech -- verbs, nouns, adjectives, etc. The modern way is to distinguish between parts of speech and the roles words play in sentences. For instance, adjectives describe nouns and they may be compared (red, redder, reddest); determiners select nouns but don't describe them (that car over there, but no thatter car). Both parts of speech, adjectives and determiners, take the role of noun modifier in a sentence. – deadrat Nov 30 '15 at 22:00

In the sentence below, the word that is a subordinator:

He demonstrated that he was true.

... in some grammars this is called a "subordinating conjunction" or a "complementizer".

The word that can also be a determinative:

  • That journey was quick.

In some grammars if the determinative that isn't followed by a noun, it is regarded as a pronoun:

  • That was quick.

It can also be an adverb:

  • I didn't realise it was that big.

Relative that

That is the dog that we saw yesterday.

That may be considered a relative pronoun by some grammars. However, a number of very important modern grammars, for example the Cambridge Grammar of the English Language regard the that which we see before relative clauses as the same that which we see in the Original Poster's example. In other words, they regard it as a subordinator in both cases.

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