The matter of materialism is an underlying outsideness, since any instance of a material thing, a table, a cup of tea, a truck, a raindrop, is eminently changeable in form and even in composition - what makes it objectively real or actual is that it is outside of and independent of the mind, and that which belongs to it and makes it so is - well, is nothing more than that very independence of mind reified to pure abstract substance. In the same way every content of mind is changeable, protean, without any fixed essence but that it belongs to the experiencing, so that it is the pure subjectivity of mind which is its underlying 'substance' or the empty background out of which it arises. These two kinds of substance are mirror images of each other and neither has a claim to reality that can be preferred to the other. Both seems to be products of the same error, an error in the way that experience is taken to be.