The phrase “blood is thicker than water” is usually taken to mean that family comes first, but its history is more complex.

It likely stems from the German proverb Blut ist dicker als Wasser, which emphasized the strength of family ties. Yet older versions tell a different story. A 12th-century text by John of Salisbury includes the line “the blood of the covenant is thicker than the water of the womb,” suggesting that chosen bonds like friendships or alliances could be even stronger than family.

By the 19th century, the modern interpretation had taken hold, reinforced by Sir Walter Scott in his 1815 novel Guy Mannering.