The Logic of 'Ought'

The two most prominent types of formalized Logic are Proposition and Quantification--the fundamental inference rule of the former is Modus Ponens, while that of that latter is Universal Instantiation.  Thus, Proposition Logic constitutes the inner structure of the consequentialist reasoning that fuels many attempts to persuade in concrete communication, i. e. that reasoning concatenates the propositions that link an entertained action to subsequent beneficial or harmful effects.  Now, insofar as it veils a threat, "You ought to do X", is a species of consequentialist reasoning, and, hence, is based on Modus Ponens.  However, Kant's insight is that in at least some cases, the 'ought' represents Universal Instantiation, i. e. entailing the concept of an individual agent as an instance of a Rational being.  Thus, contemporary Deontic Logic, derived from Modal Logic, often used to represent Kantian Pure Practical Reason, crucially distorts it.  For, Modal Logic is a species of Quantification Logic, ranging over 'Worlds', e. g. 'Necessarily P' = 'At all possible worlds, P'.  But, despite the semantic kinship of 'necessity' and 'ought', quantification in Kant's doctrine ranges essentially over agents, not over worlds.  So, whatever value Deontic Logic might have for its practitioners, it abstracts crucially from Kant's innovation.