To understand the role Kant's critical idealism has played in the development of American philosophies, one must understand why the classical American pragmatists, different realists, and other anti-ideal theorists reject Kant's critical project, no less than how idealism has been evolving in transcendental linguistics, in philosophies of history and of technology, and in ethics. This book reconstructs the little-known system of twentieth-century American philosopher John William Miller (1895–1978), who contributed to the reinvention of critical idealism in ways that might have been too radical for his own moment, but which bear importance for ours. American philosophies tend to first fix their positions by the lodestar of Kantianism, even if their goal is to move away from it. The book tracks encounters with critical idealism among the classical American pragmatists, and in more recent expressions of anti-ideal theory and object-oriented ontology. It assesses Sellars' transcendental linguistics and Korsgaard's philosophy of agency as well as pragmatist feminist reconsiderations of the source of normative commitments. Along the way, the work finds the critical project to be evolving still, albeit in ways not anticipated by Kant.