What Latin motto appeared on Niels Bohr's coat of arms?

The Latin motto on Niels Bohr’s coat of arms was “Contraria sunt complementa.”

Bohr designed the arms after Denmark awarded him the Order of the Elephant, the country’s highest chivalric order, in 1947. The shield features a taijitu, the familiar black-and-white symbol often called yin-yang, reflecting Bohr’s idea of complementarity: apparently opposing descriptions can both be necessary for understanding nature.

The motto is commonly translated as “opposites are complementary” or “contraries are complementary.” Those English versions explain the meaning, but the quiz asks for the original Latin wording. It is therefore distinct from famous Latin sayings such as “in vino veritas” and “sapere aude,” neither of which belongs to Bohr’s heraldic design.

The coat of arms connected Bohr’s scientific philosophy with his public honors. His principle of complementarity became especially associated with quantum mechanics, where wave and particle descriptions seem contradictory but each illuminates a different aspect of quantum phenomena.