If they say No, then they are asserting that to call a perception real is merely to say that it was perceived in the sense in which Sindbad did perceive a Roc: they are asserting that to call it real is not to say, in any sense, that it was really perceived: they are asserting that to call a perception real is to say that it was perceived, in some sense quite other than that in which we ordinarily use the word: for we certainly commonly mean, when we say A was perceived, that a perception of A was real we should commonly say that Sindbad did not perceive a Roc meaning that no such perception ever did exist.