How’s that then? Suppose Gombrich is Hing a NC, it doesn’t follow that anyone who can HaNC can make us see nonexistent thread; perhaps it’s necessary but not sufficient. On the other hand, maybe it is true that anyone who can HaNC can make us see things, but Gombrich is fumbling his needle- it’s just not noticeable because the thread actually exists in that case.
Either both are true, or neither.
Yeah, I spent a few minutes as I was falling asleep trying to rationalize that but don’t remember if I came up with anything sensible.
ETA: Something to do with metaphors and level-crossing.
How’s that then? Suppose Gombrich is Hing a NC, it doesn’t follow that anyone who can HaNC can make us see nonexistent thread; perhaps it’s necessary but not sufficient. On the other hand, maybe it is true that anyone who can HaNC can make us see things, but Gombrich is fumbling his needle- it’s just not noticeable because the thread actually exists in that case.
Not necessarily true. Could be that it only works in some subset of cases, of which Gombritch’s happens to be one.