Am I the only one who uses unless in completely different circumstances from if not? To me, using unless implies that an exception to the rule is being given, an edge or corner case being handled; the protasis will *usually* be false, and so the apodosis will *usually* be carried out, but on the occasion that the protasis is true, then the apodosis is skipped. In other situations, when the protasis is likely to be true a lot, I use if not. I find this semantic distinction useful, in terms of making the code more legible when I come back to it later to make changes.