How Do You Like Them Apples?

[This is an updated version of something I posted during a seminar on "constructing reality" last year]

Constructivism v. Realism

The Problem of Unconceptualized Apples

[T]he unanswerable question whether, or to what extent, any picture our senses "convey" might correspond to the "objective" reality is still today the crux of all theory of knowledge. Sextus used, among other things, an apple as an example. To our senses it appears smooth, scented, sweet, and yellow -- but it is far from self-evident that the real apple possesses these properties, just as it is not at all obvious that it does not possess other properties as well, properties that are simply not perceived by our senses. The question is unanswerable, because no matter what we do, we can check our perceptions only by means of other perceptions, but never with the apple as it might be before we perceive it.
----- E. von Glasersfeld, “An Introduction to Radical Constructivism”

Here's my best reconstruction of Ernst's rejection of realism:

1. All concepts are in the mind

2. All concepts are conceptualized

3. All concepts are concepts-of-some-x

4. All concepts-of-some-x are in the mind (from 1)

5. There can be no unconceptualized concepts-of-some-x (from 2)

6. All concepts of apples are concepts-of-some-x (from 3)

7. There can be no unconceptualized concepts of apples (from 5 and 6)

8. There can be no concept of an apple that is not a concept (truism)

9. The referent of the realist’s phrase “unconceptualized apple” is not a concept

10. There can be no concepts of unconceptualized apples (from 8 and 9) (von G.: “…we cannot possibly conceive of an unexperienced world”)

11. Metaphysical realism necessarily involves concepts of unconceptualized apples (Here’s a typical realist claim: “if every concept-user were suddenly to disappear, apples – unconceptualized and unconceptualizable – would still exist and have a determinate nature”)

12. MR is wrong and von Glasersfeld’s constructivism right (from 10 and 11)