Demonstration is also something necessary, because a demonstration cannot go otherwise than it does, ... And the cause of this lies with the primary premises/principles.
Upon the solution of this problem, or upon sufficient proof of the impossibility of synthetical knowledge a priori, depends the existence or downfall of metaphysics.
I find my breath gets short, but it seldom gets longer as a man gets older. I take it as it comes, and make the most of it. That's the best way, ain't it?