Deep Truths Are Statements in Which the Opposite Also Contains Deep Truth

Niels Bohr? Hans Bohr? Werner Heisenberg? Oscar Wilde? Emilio Segrè? Carl Sagan? Anonymous?

Dear Quote Investigator: A famous scientist once asserted something like this:

The opposite of a deep truth is another deep truth.

Would you please help me to find a citation and the correct phrasing?

Quote Investigator: In 1949 the prominent physicist Niels Bohr published an essay titled “Discussion with Einstein on Epistemological Problems in Atomic Physics” which included a passage about “deep truths”. Boldface added to excerpts by QI: 1

In the Institute in Copenhagen, where through those years a number of young physicists from various countries came together for discussions, we used, when in trouble, often to comfort ourselves with jokes, among them the old saying of the two kinds of truth. To the one kind belong statements so simple and clear that the opposite assertion obviously could not be defended. The other kind, the so-called “deep truths,” are statements in which the opposite also contains deep truth.

Bohr labeled the remark a joke, and he used the phrase “old saying”. Thus, he disclaimed authorship; nevertheless, he usually receives credit for the statement.

Below are additional selected citations in chronological order. The phrasing of this notion varies; hence, this section begins with an overview:

Continue reading Deep Truths Are Statements in Which the Opposite Also Contains Deep Truth


  1. 1959 (1949 Copyright), Albert Einstein: Philosopher-Scientist, Edited by Paul Arthur Schilpp, Chapter 7: Discussion with Einstein On Epistemological Problems in Atomic Physics by Niels Bohr, Quote Page 240, Harper Torchbooks, Harper & Row, New York. (Verified with scans)