The three synthesis are necessary components in the experience of space and time. These three points which are a priori explain the concept of understanding which is necessary for experience to take place. .
The Synthesis of Apprehension in Intuition begins with the notion that our representations, ideas and concepts otherwise known as knowledge, belong to inner sense. This is true whether the origins of these representations are a priori or empirical because they are both modifications of the mind. Assuming this to be true, our representations are also subject to time, because time is a formal condition of inner sense. Kant states that this is a condition that s fundamental to what follows. .
He continues in stating that if our awareness didn't hold together different concepts, then we wouldn't be aware of things. Things, representations, are held together in time, in the mind. They come together to form a whole.
As long as the concept of time is assumed, it is possible to have a series of "impressions" in the mind. And in order for these to mean anything, they must have unity. This is what makes it possible in any single moment to comprehend a concept to which those impressions belong. Kant named this the Synthesis of Apprehension because it relates to intuition which contains a manifold. Lastly it is to be understood that this synthesis is a priori. This is because if it were not then we would not have the concepts of space and time on which all these concepts rest. This first synthesis could be looked at as establishing the function of understanding through intuition. It is to be directly related to the second synthesis.
The Synthesis of Reproduction in Imagination begins with saying it is an empirical law for representations sequenced through time to be associated with each other. Even in absence of one the mind can realize the other due to this rule. Although this misses the point of the synthesis it is helpful in what follows.
