Are there some issues on which it is equally rational to defend two opposite positions? (Whisper: "Free will debate.")
Kant famously argues that reason grapples with itself, so that its very nature and pretensions have to come under stern critique. Perhaps flouting our expectations, he is extremely specific about the topics on which this grappling is unavoidable. It turns out that there are only four - at least where the description of reality is concerned - and they all concern questions of cosmology, or the composition and behavior of objects in nature.
The composition, the division, the origination, and the dependence of all things are topics that we cannot help finding interesting, even pressing (if we are students of nature, i.e. scientists) - they are also topics which tend to reduce philosophers to raving helplessness and pointless conflict. Crucial to Kant's exposition is that, for each of these, a more or less ironclad case is available for two opposite conclusions.
What is to be done about this? What does this tell us about our powers and limitations as knowers and thinkers? Rather than relying on the text of Kant, we will talk through those supposedly ironclad arguments that he sees in play.