Vortrag am 10.Kongress der Österreichischen Gesellschaft für Philosophie, Innsbruck 2015. http://www.uibk.ac.at/ipoint/blog/1326563.html

Metaphysical realism holds that (much of ) the world is mind independent and that truthis correspondence between thought and the world. Idealism is opposed to this; one important motivation driving it is an argument to the effect that metaphysical realism mustinevitably succumb to global skepticism. It goes roughly like this: “We cannot step outsideour own minds to compare our thoughts with mind-independent reality. Yet, on therealist view, this is precisely what we would have to do to gain knowledge of the world.We would have to access reality as it is in itself, to determine whether our thoughts correspond to it. Since this is impossible, since all our access to the world is mediated by ourcognition, realism makes knowledge about the world impossible. Since knowledge aboutthe world is possible, realism must be wrong.” I call this “the idealist master argument”.A version of it was given by Kant: “According to [the correspondence definition of truth]my cognition, then, to pass as true, shall agree with the object. Now I can, however, compare the object with my cognition only by cognizing it. My cognition thus shall confirmitself, which is yet far from sufficient for truth. For since the object is outside me and thecognition in me, I can judge only whether my cognition of the object agrees with my cognition of the object” (Kant, Logic, introduction vii). This sort of argument has been veryinfluential across a wide spectrum of philosophical traditions. As I see it, it is a fusion andelaboration of two earlier arguments mainly due to Berkeley. The first was: “Realism isincoherent, because one cannot conceive a thing which is unconceived”—later condensedinto the notorious formula: “No object without a subject”. The second was: “Realismleads to skepticism, because only ideas can resemble/be compared with ideas”. Once these are elaborated into the master argument, we can distinguish two parts. Part (A) saysthat there is something we cannot do, namely ascertain a correspondence between ourthoughts and reality. Part (B) says that we have to do it, on a realist correspondence account of truth, if we are to obtain knowledge. With respect to part (A), one should lookinto the use the argument makes of terms like “accessing” and “comparing”. Do we everliterally have to compare thoughts with the world to ascertain correspondence? If so, howoften is this necessary? And is it really that hard? With respect to part (B), one should ask:If truth were correspondence between thought and reality, would it follow, as the argument seems to assume, that in order to know that p one has to ascertain that one’s beliefthat p corresponds to reality?