Husserl’s Synthetic A Priori Argument From Mereology

A Response to Kant’s Metaphysical Challenge

By: Jay Dyer

Modern philosophy since Immanuel Kant has tended to deny the possibility of making a synthetic a priori claim about experience. An analytic statement is one in which the concept of the predicate is contained in the subject. Synthetic statements are not this way; here, the predicate is not contained in the meaning or definition of the subject and additional information may be added, based upon experience. Such was Kant’s argument in his Prolegomena to any Future Metaphysics. Thus, Kant thought, no necessary, a priori laws of experience could be posited—which are themselves the foundations of metaphysical claims, and, without these, he proclaimed, metaphysics was no longer possible. The purpose of this paper is to present Husserl’s argument from mereology for synthetic a priori truths of experience.

Mereology is the logic of the relationship of parts to wholes. In Husserl’s 1901 Logical Investigations, Volume II, “Investigation III” takes up the topic of mereology, following Brentano’s lead. Here, Husserl thinks, necessary a priori truths about experience may be given. A “part,” Husserl argues, is anything which can be distinguished in an object, such as color, shape, or extension, in contrast to the intentional object as a whole. However, an important distinction must be made: some parts are independent, while others are dependent. A dependent part is defined according to “its inability to exist by itself.” That is, “non-independent objects are objects belonging to such pure Species as are governed by a law of essence to the effect that they only exist, if at all, as parts of more inclusive wholes of a certain appropriate Species.”

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.


Works Cited

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).

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