  Of greater relevance was his suspicion of the move from conceivability to possibility, and inconceivability to impossibility, thinking that answers to questions about conceivability were dependent upon the state of knowledge and imaginative powers of the person entertaining them. Was it inconceivable that Caesar (the Julius of old) be non-human? Ayer thought it consistent with everything he knew of Caesar (apart from his being human) that Caesar was a robot, so he could “easily conceive of it as a possibility” (“Replies” p. 308). On the other hand, if asked whether Caesar was a tortoise, he would suspect that the word “Caesar” was here used with a different reference in mind. Ayer buttressed this thought by suggesting that the descriptions securing the referent of the term “Caesar” would normally make it logically inconsistent that the satisfier of the descriptions be a tortoise, but that this did not establish de re necessities; it does not follow that the Caesar in question necessarily satisfies the descriptions associated with the use of the name. To the suggestion that something other than descriptions might secure the proper reference, such as the causal origin of the use of the term, Ayer was dismissive: “…the idea …that one can explain the nature of reference by saying that what makes A’s use of a sign s a reference to an object O is its causal derivation from someone’s original use of s to refer to O is a manifest absurdity. If one does not understand what it is for s to refer to O, one is none the wiser; and if one does, the causal flummery is otiose.” (“Replies” 1979 p. 309.)