B’s argument probably commits the Straw Man Fallacy:    A: S…

B’s argument probably commits the Straw Man Fallacy:    A: Since Kant’s Critique of Practical Reason does not attempt to find foundational grounds for the authority of reason as a source of moral truth, we can conclude that he changes course from his Groundwork strategy for relating freedom and morality.   B: None of that follows; there are no legitimate grounds for believing that Kant fails to establish any common grounds between the Critique and the Groundwork.  His account of respect, for instance, is importantly continuous.