Credit and interest

La caution solidaire is a human being who signs for somebody else’s debt, and the first word of it is one English uses every day for something quite different. Both go back to Latin cautio, and cautio is built on cavere, to be on one’s guard. In Roman law a cautio was not a feeling at all: it was the written security a party gave, the undertaking that made a promise enforceable. French kept that half of the word. La caution is the person or the sum standing behind an obligation, se porter caution is to go surety for somebody, and sujet à caution, said of a claim, means it needs backing before anyone should believe it. English took the other half, the wariness out of which the security grew: « caution » is care, « to caution » is to warn, « precaution » is praecautio, and « caveat » is cavere itself in the subjunctive, let him beware. One Latin verb, then, gave one language a guarantor and the other an alarm bell — so a French contract that names la caution is naming a person, not sounding a warning.