That that is is that that is not is not is that it it is
The sequence can be understood as either of two sequences, each with four discrete sentences, by adding punctuation:
That that is, is. That that is not, is not. Is that it? It is.
That that is is that that is. Not is not. Is that it? It is.
This relates a simple philosophical proverb in the style of Parmenides that all that is, is, and that anything that does not exist does not. The phrase was first noted in Brewer's Dictionary of Phrase and Fable.
A similar sequence, consisting of only one sentence and no punctuation, is:
That that that is that that is not is not that that is that that is is not true is not true.
Which can be made clearer by the use of synonyms and punctuation:
The idea, that the statement "what is that, which does not exist, is not that, what is that, which exists" is false, is incorrect.
The part enclosed in the quotation marks is true: it essentially says that what does not exists is not the same as what exists. The phrase as a whole then rightly notes, that a statement claiming that the part enclosed in the quotation marks is false, is itself incorrect.
There is a slightly longer construct following a similar pattern:
That that is is. That that is not is not. That that is not is not that that is. Is that not it? It is.
Another similar sequence, consisting of three graphic sentences and punctuation:
That "that is" is that "that is not" is not. Is that it? It is.
Meaning: Saying that something exists is stating that "that same thing is nonexistent" is false.
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- List of linguistic example sentences