Universality and Necessity in our Experience of Objects
Kant draws our attention to certain features of our representations of objects that, in his view, will serve to defeat associationism and establish a priori synthesis:
The transcendental unity of apperception is that unity through which all the manifold given in an intuition is united in a concept of the object. It is therefore entitled objective, and must be distinguished from the subjective unity of consciousness… Whether I can become empirically conscious of the manifold as simultaneous or as successive depends on circumstances and empirical conditions. Therefore, the empirical unity of consciousness, through association of representations, itself concerns an appearance, and is wholly contingent… Only the original unity is objectively valid: the empirical unity of apperception,… which… is merely derived from the former under given conditions in concreto, has only subjective validity. One person connects the representation of a certain word with one thing, the other [person] with another thing; the unity of consciousness in that which is empirical is not, as regards what is given, necessarily and universally valid. (B139–40)
For Kant, a defining feature of our representations of objects is their objective validity. For a representation to be objectively valid it must be a representation of an objective feature of reality, that is, a feature whose existence and nature is independent of how it is perceived (Guyer 1987:11–24). In this argument, it appears that Kant just assumes that the representations that make up experience are objectively valid. He then aims to establish that association is inadequate because it can yield only representations that are not objectively valid. In the above passage, Kant contends that our objectively valid representations must in a sense be necessary and universal. However, the empirical unity of consciousness, which involves an ordering of representations achieved by association, can only be non-universal, contingent, and hence merely subjectively valid, by contrast with the transcendental unity of apperception, which involves an ordering that is universal and necessary, and is therefore objectively valid. In Kant's conception, it is the fact that the transcendental unity of apperception is generated by a priori synthesis that allows it to yield an ordering that is universal, necessary, and objectively valid. (Ameriks 1978, Pereboom 1995, Patricia Kitcher 2011:115-60; Allais 2011)
Subjective Validity and Objective Validity
Subjective Validity is bias opinion, which a person will consider them as a statement to believe in if the opinion is significant or meaningful to them. It is based on their experiences that a person had gone through. Subjective Validity is more of a posteriori judgment where they are dependent on experience and empirical evidence. An example would be a dream that only happens in a person's brain, but never existed or happened in real life.
Objective Validity is a priori judgment according to Kant, which they are independent of experience. The way Kant uses the term experience differs from existing usage in the degree experience, understanding in its modern use, must be objective validity in order to classify as experience in Kant's sense. This means that he is making the experience possible (real); they must have a truth value, which do not have to be 100% true. He talks about something is only a judgment if it is objective validity, otherwise it might have a well formed of judgment.
According to Kant, appearance is pure concepts on understand. "Now reason clearly sees: that the sensible world could not contain this completion, any more than could therefore all of the concepts that serve solely for understanding the world: space and time, and everything that we have put forward under the name of the pure concepts of the understanding. The sensible world is nothing but a chain of appearances connected in accordance with universal laws, which therefore has no existence for itself; it truly is not the thing in itself, and therefore it necessarily refers to that which contains the ground of those appearances, to beings that can be cognized not merely as appearances, but as things in themselves." (105)