Somewhere outside of him and apart, as if he were reading it in a brain not his own, he observed the thought that there was some flaw in the scheme of the punishment she wanted him to bear, something wrong by its own terms, aside from its propriety or justice, some practical miscalculation that would demolish it all if discovered.
There are no more uses of "propriety" in the book.
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While she took comfort in propriety, he saw it as a straitjacket.
She was known for losing all sense of propriety once she had a few drinks.