that
It is true for all that that that that that that that refers to is not the same that that that that refers to.
The sentence is a meta-linguistic puzzle: even granting the truth of all the surrounding clauses, what one 'that' refers to differs from what the other 'that' refers to — using 'that' simultaneously as demonstrative, relative, and conjunction.
Meanings (pronounced /ðæt/)
indicating something specific previously mentioned or readily understood
- That is my favorite book.
- I'd like that one, please.
introducing a clause that defines or modifies a noun
- The book that I read was excellent.
- Anyone that finishes early may leave.
introducing a clause that is the object of a verb of saying or thinking
- She said that she would come.
- I believe that we will succeed.
Word origin
From Old English þæt, the neuter form of the demonstrative þe/þæt/sē ('the, that'), from Proto-Germanic *þat. The same word in Modern English serves as demonstrative pronoun ('that book'), demonstrative adjective ('that one'), relative pronoun ('the book that I read'), and subordinating conjunction ('I think that you're right'). All four senses descend from the same Old English source.
Fun fact
The famous 'that that that that' sentence works because English uses the single word 'that' to do at least four different grammatical jobs. Linguists count 'that' among the most overworked function words in English — only 'the', 'a', 'of', 'and', and 'is' beat it for sheer frequency, and none has more grammatical roles.