How do you punctuate the following so that it makes proper English sense: "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.

That that is is that that is not is not is that it it is is an English word sequence demonstrating lexical ambiguity. It is used as an example illustrating the importance of proper punctuation.

The sequence can be understood as four discrete sentences by adding punctuation:

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 but was popularised when the 1959 short story "Flowers for Algernon" was adapted for the big screen in 1968 as Charly.

See also:

Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo

James while John had had had had had had had had had had had a better effect on the teacher

https://en.wikipedia.org/wiki/That_that_is_is_that_that_is_not_is_not_is_that_it_it_is