§61

Thing in itself means that which exists independently of our perception, hence that which actually is. For Democritus it was formed matter, and basically it was the same thing for Locke; to Kant it was = x, to me will.

How Democritus took the issue entirely in this sense and therefore stands at the top of this arrangement, is demonstrated by the following passage from Sextus Empiricus (Against the Mathematicians, Book III, § 135) who had his works in front of him and often quotes from them verbatim: ‘But Democritus denies what appears to sense perception and asserts that nothing of it appears as it is in truth, but instead only as it seems to us; in truth however what actually is present is the existence of atoms and the void.’ I recommend the entire passage be read, where later we also find: ‘In reality therefore we do not know how a thing is constituted or not constituted’, also ‘How everything is constituted is in truth difficult to know’.

All this simply states that ‘we do not know things according to what they may be in themselves, but instead merely as they appear’, and it opens that series that originates from the most decisive materialism but leads to idealism and concludes with me. We find a strikingly clear and distinct separation of the thing in itself from appearance in a passage in Porphyry which Stobaeus has preserved for us in the forty-third chapter of his first book, fragment 3. It reads: ‘When it is said of the sensual and material that it is pulled apart from all sides and is changeable, then this is actually the case … But what is valid for that which actually is and exists in itself is that it is eternally grounded in itself and likewise that it always remains the same to itself etc.’ (Stobaeus, vol. II, p. 716.)

§62

Just as we know merely the surface but not the great solid mass of the interior of the globe, so too we know empirically of the things and of the world generally nothing but their appearance, i.e., their surface. The precise knowledge of these things is physics in the broadest sense of the word.