Pulling Lincoln's Leg: Or, Is the World Greek* or German*?

This talk concerns the (perhaps never-ending) debate between realism and constructivism. Philosophical constructivism is the view---a descendant of Kant's view and idealist views more generally---that physical reality is somehow "created" or "constructed" by the imposition of concepts or mental structure onto an *unstructured* world---an amorphous noumenal glub. For example, space and time are, for Kant, "constructed". Realism denies this, and regards the external world as intrinsically structured, prior to and independenlty of any cognitive representation by humans.

Half-jokingly, I use the labels "Greek*" and "German*" to characterize the realist and constructivist views, respectively. By and large, the pre-Socratics, as well as Plato and Aristotle, were realists in the above sense (as is common sense, and virtually all scientists), while German philosophy since and including Kant has been steeped in a variety of subjective, social, linguistic and cultural constructivism (idealism). A vivid illustration of the difference between realists and constructivists is their response to the Lincoln Leg Puzzle (often attributed to Abraham Lincoln):

How many legs does a cow have? Four.

If we also call its tail a 'leg' how many legs does it have? Five?

No, calling a tail a 'leg' doesn't make it a leg!

In a rather clear sense, the realist will answer "four" to Lincoln's leg puzzle, while the constructivist will insist that the answer is "five". This is because when a realist imagines other but nearby possible worlds, they keep the *natural or inherent structure* constant even if, as we do in this case, we change the semantic meanings of words. On a constructivist view, there simply is no inherent or instrinsic structure to be kept constant, so the cow jumps from having four legs to five legs, and purely because of a relabelling---a difference in the way it is *represented* (described, etc.). The realist intution is that relabelling makes no difference. I want to use this as a starting point for discussing a number of issues dividing the realist (Greek*) view from the constructivist (German*) view(s), and in particular, the central issue of whether external reality is intrinsically or inherently structured (i.e., mind-independently) or whether structure only arises as a kind mental projection (whether from a species-universal system of a priori categories (Kant) or socially-culturally determined, as in the case on modern social constructivism).