Independent parts may, conversely, be sensibly spoken of as existing in isolation, without a fixed substrate, whether in imaginary or actual isolation. Husserl gives an excellent example of this in reference to color. He writes,
A head can certainly be presented apart from the person that has it. A color, form, etc., is not presentable in this fashion, it needs a substrate, in which is can be exclusively noticed, but from which it cannot be taken out.
Thus, Husserl argues, there can be no experience of independent color or form (shape), apart from an object of some kind, acting as its substrate. Following upon these lines, Husserl explains that there are foundational parts, in which it is posited that if A cannot be without B, then A requires the foundation of B. So, for example, extension in space requires some body upon which extension is predicated or founded. Extension cannot be without a substrate, and therefore substrata are foundational for extension. Likewise, a color cannot exist without some space that it covers.
With that in mind, it becomes clear that “red,” for example, would be a non-independent part of anything “colored.” “Redness” must have as its substrate some object as its foundation, as it is never the case that one experience’s “redness” without a foundational object of some kind. Likewise, “shape” and “extension” are never experienced apart from some object upon which these qualities are based. These facts, then, are clearly a priori. In other words, they are universally necessary, as we are constituted as humans to experience reality in this fashion. These facts, however, are also not truths bound up in the definition of color or extension or shape; they are thus synthetic. They tell us something about our experience—metaphysical facts about our experience.
In conclusion, Kant’s challenge was as follows,
If anyone thinks himself offended, he is at liberty to refute my charge by producing a single synthetic proposition belonging to metaphysics which he would prove dogmatically a priori; for until he has actually performed this feat, I shall not grant that he has truly advanced science, even though this proposition should be sufficiently confirmed by common experience.
Husserl, by a simple and yet profound analysis of mereology, has emphatically answered Kant’s charge by producing a single synthetic a priori claim (and several more) pertaining to experience: namely, that our experience, particularly in the realm of parts and wholes, exhibits consistent, law-like, and necessary regularities.
Blackburn, Simon. Oxford Dictionary of Philosophy (Oxford University Press:
New York, NY, 1994).
Husserl, Edmund. Logical Investigations, Vol. II (Routledge: New York, NY,
Kant, Immanuel. Prolegomena to any Future Metaphysics (Hackett Publishing
Company: Indianapolis, IN, 1977).