Reason and Sufficient Reason

The Principle of Sufficient Reason is generally considered to be a description of how Reason functions, with, according to Schopenhauer, four varieties, one of which is Physical Causality, the formulation of which is: Everything that occurs is the effect of a preceding cause that sufficiently determines it.  But, the Principle can be normative, as well, in two different ways.  First, it can emphasize the criterion of Sufficiency in the specific use of Reason, one significant application of which is to Hume's concept of Causality, since Constant Conjunction does not explain Sufficiency.  Second, it can similarly apply to the use itself of Reason--requiring sufficient grounds for any use.  For example, according to Kant, the measure of Sufficiency is Universality, so any use of Reason that is not Universalizable is insufficiently Rational.  But that formulation is nothing other than that of his Principle of Pure Practical Reason, i. e. is the Principle of Sufficient Reason applied to Maxims of behavior, e. g. to notably  Hume's concept of Instrumental Reason.  But, having established an autonomy of Reason, one which arguably every Philosopher, even the Skeptic, adheres to, he attempts to further derive a concept of a deity from autonomous Reason--one which rewards Rational behavior.  However, if a deity is required to reward Rational behavior, then the latter is in itself insufficient to that end, and, hence, violates the Principle of Sufficient Reason.  Kant thus squanders an insight with potentially radical consequences.