Causa sine qua non
A particularly elegant Latin phrase meaning the effective cause: literally, the “cause without which there would be nothing”. Where there are several contributing factors to some kind of perfidy, lawyers will often be obliged to identify which ones are suitable subjects for legal warfare. The causa sine qua non is just such a subject.
An example[1] will suffice.
A inhouse lawyer has been out to a law-firm cocktail function and crossed that imperceptible threshold — the schwarchild radius of alcohol consumption — beyond which the discretion, judgment and common sense which would usually guide him safely home to bed in time for work in the morning ceases to operate. He finally made it back to base at 4 a.m.
As luck would have it, he has arranged to be late into the office, for it is his daughter’s school assembly in the morning. The theme is gender equality in modern Britain, but there will be a brief interlude for a song about spiders.
Is the school assembly the causa sine qua non of his absence from that dreary 9 a.m. meeting? If it pleases your honour, I humbly submit it is not.
Plain English Anatomy™ Noun | Verb | Adjective | Adverb | Preposition | Conjunction | Latin | Germany | Flannel | Legal triplicate | Nominalisation | Murder your darlings