
As quoted by his son Hans Bohr in "My Father", published in Niels Bohr: His Life and Work (1967), p. 328
Unsourced variant: The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
As quoted in Max Delbrück, Mind from Matter: An Essay on Evolutionary Epistemology, (1986) p. 167. It is the hallmark of any deep truth that its negation is also a deep truth