The confusions of Kripke

Abstract

Professor Putnam has recently argued1 that if there were brains in vats, what they would be saying when they said that they were brains in vats would be false, and so that there were brains in vats would imply its own falsity, and so be false ((p-+ ?p)? ?p). In a recent article in Erkenntnis2 I argued that, even if what a brain in a vat would be saying when (he, she or) it said that it was a brain in a vat were false (which it would not necessarily be) this would not show that it was both true and false that it was a brain in a vat. This is because, if the proposition that a brain in a vat is asserting when it says that it is a brain in a vat is the proposition that it is an image brain in an image vat, this proposition is not the contradictory of the pro? position I am asserting when I say that it is a brain in a vat. There is therefore not one proposition, asserted both by me and by a brain in a vat, which is such as to be false if it is true. Putnam's mistake arises from confusing a brain in a vat's uttering the sentence T am a brain in a vat' with its asserting the position that it is a brain in a vat. It would not be asserting this proposition, if Putnam is right in thinking that by 'brain' it meant 'image brain' and by 'vat' it meant 'image vat'. Professor Kripke has maintained3 that there is a class of contingent propositions that may be known a priori. For example, the metre rod in Paris might have been shorter than it is. Hence that the metre rod in Paris is a metre long is a contingent proposition. We know a priori that it is a metre long, however, because the word 'metre' is a name for that length which, it so happens, is the length of the metre rod in Paris. I agree with Kripke that the metre rod in Paris might have been shorter than it is. If the hand of the craftsman who made it had slipped, as it might have done, then it probably would have been less than a metre long. I do not agree with Kripke, however, that we know a priori that it is a metre long.