Hi lathlee,
Yes, it's certainly possible to read the first sentence as a nested conditional, though both Jonathan and James's explanation posts in this thread cut through that nested relationship in a way I find very helpful.
What you're seeing correctly is that there's a full conditional statement before the "except" in that first sentence, which is "Any government practice that might facilitate the abuse of power should not be undertaken," i.e.
Might Facilitate Abuse
~Undertake.
The "Unless" formula (which also applies to "except" statements) would require us to negate that entire conditional and make it the sufficient condition for the except portion of the statement.
~(Might Facilitate Abuse
~Undertake)
Compelling Reason.
The sufficient condition resulting from that diagram is a bit of a beast to understand, but what it's essentially saying is "If it's not the sort of situation where the practice might facilitate abuse and you should not undertake it," in other words "If it's a situation where you SHOULD undertake the practice even though it might facilitate abuse."
So, the diagrams Jonathan and James arrive at in their explanations are the best (and simplest) understanding of that relationship, which in essence amounts to "If you undertake a government practice that might facilitate abuse of power, then you must have a compelling reason to do so."
I hope this helps!
Jeremy
Jeremy Press
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