“Kullu mumkin ʿādatan mumkin ʿaqlan, wa-lā yanʿakis”
Whatever is customarily possible is rationally possible, but not conversely.
That is why the classification contains three standard categories, not four. “Customarily possible but rationally contradictory” is not a distinct legitimate category: ordinary possibility presupposes rational coherence.
Rational possibility, however, does not guarantee customary possibility. Ighrāq relies on precisely this difference: the described event remains conceivable without contradiction while exceeding ordinary causal expectation.