I perceive that appearances follow one another. Thus I am connecting two perceptions. This is a synthetic faculty of imagination. The objective relation of appearance of succession is not determined through perception. In order that this relation be known as determined, it must be so thought that it is thereby determined as necessary which came first.
Necessity can only come from a pure concept of understanding.
In this case it is cause and effect. The apprehension of the manifold of appearance is always successive. Appearances, simply in virtue of being representations, are not in any way distinct from their apprehension. We do not know if the parts of the object follow one another. This is arbitrary succession.