Full Idea
The two readings of Kant depend on whether the world of phenomena is 'constrained' by the noumenon, or whether it is 'free-floating'.
Clarification
The 'noumenon' is unexperiencable reality
Gist of Idea
Kant is read as the phenomena being 'contrained' by the noumenon, or 'free-floating'
Source
comment on Immanuel Kant (Critique of Pure Reason [1781]) by Marianne Talbot - talk
A Reaction
The free-floating reading leads to idealism, since the noumenon then becomes a quite irrelevant part of Kant's theory, and can be dropped (since its existence means nothing if it has no causal role). On the first reading, constraint becomes interesting.