Sine qua non (pronounced "seenay kwaa non") or conditio sine qua non (plural sine quibus non) was originally a Latin legal term for "(a condition) without which it could not be" or "but for..." or "without which (there is) nothing." It refers to an indispensable and essential action, condition, or ingredient.
It was as though he knew very well that in Lombard’s past actions legality had not always been a sine qua non .
Agatha Christie -- And Then There Were None
Simple facts in isolation, and facts to connect them—ands and buts—are the sine qua non of all their glorious achievement.
John Gardner -- Grendel
He soon found that freedom from fear of arrest was not the sine qua non of his existence.
Theodore Dreiser -- Sister Carrie
This was normally a sine qua non of career advancement in all of the Soviet armed services.
Tom Clancy -- The Hunt for Red October
—Still it’s solid food, his good genius urged, I’m a stickler for solid food, his one and only reason being not gormandising in the least but regular meals as the sine qua non for any kind of proper work, mental or manual.
James Joyce -- Ulysses
I believe in the people and am always glad to give them their due, but I am not for spoiling them, that is a sine qua non .
Fyodor Dostoyevsky -- The Brothers Karamazov
If it had not already been so, race became the sine qua non of South African society.
Nelson Mandela -- Long Walk to Freedom
Looking back, Deo felt she was both beloved and ridiculed by neighbors, because she was always giving things away, such as milk and especially salt, the sine qua non of the local cuisine, sold by the pinch in the markets.
Tracy Kidder -- Strength in What Remains
That is a sine qua non.
E.M. Forster -- Howards End
Yes, it was the kind of event that might be termed a "miracle"—except that nothing happened; the laws of nature weren’t suspended (which Matron felt was the sine qua non for miracles).
Abraham Verghese -- Cutting for Stone
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She had the surface attributes of that precarious profession-striking features, a commanding presence, the sine qua non that forced both men and women to fall silent and pensively appraise her when she walked down a street or entered a room.
Robert Ludlum -- The Bourne Ultimatum
In the nature of single blessedness he would one day take unto himself a wife when Miss Right came on the scene but in the interim ladies’ society was a conditio sine qua non though he had the gravest possible doubts, not that he wanted in the smallest to pump Stephen about Miss Ferguson (who was very possibly the particular lodestar who brought him down to Irishtown so early in the morning), as to whether he would find much satisfaction basking in the boy and girl courtship idea and