Notice that the proof for necessity e-conversion depends on possibility i-conversion, and the proof for possibility i-conversion on necessity e-conversion. Alternative proofs could be proposed; for e-conversion, for example, one could argue that “no J is possibly B” converts to “no B is possibly J”, if not, then “some B is possibly J”, but this with the first proposition produces by Ferio “some J is not possibly J”, which is absurd. This proof is open to Avicenna, given that he took first-figure syllogisms with a possibility proposition as its minor premise to be perfect, or nearly so; this syllogistic mix was rejected by most later logicians, along with the other proofs.