Unity is more fundamental than synthesis, since it is a component of the concept of a unified manifold, which is what synthesis brings about. The unity presupposed by synthesis is not the category of unity, because the concept of a category presupposes that of unity as well. (Critique of Pure Reason Lecture Notes: Transcendental Deduction G. J. Mattey)

The first sentence seems unclear to me. How is unity more fundamental than synthesis? The second sentence also is confusing. What is not the category, "synthesis" or "unity"? My search into the definition of category used by Kant did not help me unravel the puzzle for.

  • You've tagged this "metaphysics" but it's really most centrally about Kant (And his epistemology). Do you want the tag metaphysics?
    – virmaior
    Commented May 24, 2016 at 23:52

2 Answers 2


If the goal of synthesis is a unity, then, as a goal, unity must pre-exist even the concept of synthesis, and is therefore more fundamental.

Unity is the category. Categories are meant to be foundational to all forms of thought, including those beyond humanity.

Two cases of potential thought beyond humanity come to mind:

1) traditional Angels, who are very much like humans (both being images of God) but with none of the limitations of physics, and

2) intelligent animals quite different from humans, with no exposure to, for instance, verbal language.

(I don't necessarily believe in either of these. Nor are the explicitly approved by Kant. But they are good theoretical test cases. And my suspicion, given his era and his background is that he believed in both of them.)

Angels, not being bound by time, would not do synthesis, their thinking would be immediately correct. But they would, in their obedience to a single God, have the underlying concept of Unity.

Aliens would have to learn. So they would do synthesis. And in order to perpetuate themselves, they would have to recognize themselves as a species, so they would also have the concept of Unity.

So Unity wins, it can be a category. Synthesis cannot.


The unity that is presupposed by all of our experience is the unity of the self, i.e. the unity of apperception which makes possible the "I think." Without this foundation of unity, we would have no experience to call our own, and consequently we would have no basis for the conception of ideas nor for the possibility of any thought whatsoever:

"The 'I think' must accompany all my representations, for otherwise something would be represented in me which could not be thought; in other words, the representation would either be impossible, or at least be, in relation to me, nothing." (Critique of Pure Reason, B131)

The idea of unity comes up in various contexts in Kant's writing. There is the unity of propositions, the knowledge of which is made possible by the synthesis of a subject with its predicate; there is the unity which is necessary for the formation of concepts; there is the unity of events through time; there is the unity which unites objects in a single space; and, as already mentioned, there is the unity of apperception which makes all of these others possible.

Due to the fact that unity is the most fundamental principal all of our mental existence, it's difficult for us to imagine what it would be like without it. One way to illustrate it is with the idea of afterimages which occur when a bright light is shined in one's eyes. The afterimage exists simultaneously with our perception of the world, and the mind doesn't unite these two perceptions because we don't attribute the same objective reality to the afterimage as if it were some real object in the physical world. I believe that this may help us understand what Kant meant when he said the following:

"Substances (in the world of phenomena) are the substratum of all determinations of time. The beginning of some, and the ceasing to be of other substances, would utterly do away with the only condition of the empirical unity of time; and in that case phenomena would relate to two different times, in which, side by side, existence would pass; which is absurd. For there is only one time in which all different times must be placed, not as coexistent, but as successive." (Critique of Pure Reason, A188/B231)

Although he is speaking of time, it's hard to imagine what could be meant by the existence of more than one time. It's easier, I think, to think of the existence of more than one simulaneous reality as illustrated with the idea of the afterimage. The rules which govern separate realities would be completely independent of one another, so it would be like having different times, the flow of events having no unified coherence. Now, if you multiply this idea by infinity, you get an idea of how essential the unity of apperception is. What I mean by that is that our experience is made up of an innumerable amount of individual elements. Our field of vision, for example, can be thought of as consisting of pixelated point that we see simultaneously as a whole. Without unity of perception, there would be no coherent structure for those points to coexist, and without unity of apperception, no two point could be experienced at all. Each element of experience would be epistemically isolated from all the others.

Now, concerning your question about unity preceding synthesis, the process of forming concepts occurs in a number of steps. First, we receive intuitions or impressions from the senses, and this "manifold" is united by the imagination. However, the unity that results from the imagination is only a pre-conceptualization, because it cannot be presupposed to conform to reality. Therefore, a synthesis governed by the understanding is necessary to form concepts which are judged to be consistent with reality. When intuitions are brought together under concepts, Kant refers to them as cognitions (Erkenntnis) due to the fact that they are objectified according to the rules of judgement. Now, since the idea of unity is itself a concept, it cannot be the same as the unity that makes conceptualization possible:

"This idea of unity, therefore, cannot arise out of that of conjunction; much rather does that idea, by combining itself with the representation of the manifold, render the conception of conjunction possible. This unity, which a priori precedes all conceptions of conjunction, is not the category of unity; for all the categories are based upon logical functions of judgement, and in these functions we already have conjunction, and consequently unity of given conceptions." (Critique of Pure Reason, B129)

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