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"是一个表达歧义性以及标点符号的重要性的英文短语。
这句“句子”可以通过增加标点符号来分拆成四个句子：
That that is, is. That that is not, is not. Is that it? It is.

(存在的就是存在的，不存在的就是不存在的。就是这样吗？是。)
还有一个分拆方法：
That that is is that that is. Not is not. Is that it? It is. (那存在的就是那存在的，不是(存在)的就不是(存在)。就是这样吗？是。)
这是一个巴门尼德式的哲学谚语“that all that is, is, and that anything that does not exist does not.(存在的就是存在的，其他所有不存在的就是不存在的。)”这一个短语首先在Brewer's Dictionary of Phrase and Fable里出现，但在1959年的短故事"献给阿尔吉侬的花束(Flowers for Algernon)"变得有名。Garylin(吉里连)在躺在草地上采摘雏菊以及自言自语时注意了它。

变体

一个类似的短语，只有一句句子和一个标点符号：
That that is is that that is not is not that that is that that is is not true is not true.
意思：那个‘这句句子“那似乎不存在的与那存在的不同”是错的。’的想法是不对的。
还有一个类似的，长一些的短语：
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.

(那存在的就是存在的，不存在的就是不存在的，那不存在的不是那存在的。这样不是那样吗？是。
还有一个有三句句子的短语：
That "that is" is that "that is not" is not. Is that it? It is.

(那“这存在”就是相等于“这不是”是错的。就是这样吗？是。)
意思：说某东西存在就等同说“那不存在”是错的。