Some thought him to be a skeptic, others held he was the savior of religious faith. Some successors to Kant, such as Schiller, Fichte, Schelling, and Hegel, made philosophy the time honored mental discipline. Kantian epistemology needed to be developed. The Kantian dualism of the intelligible and phenomenal worlds, freedom and mechanism, form and matter, knowledge and faith, practical and theoretical reason, presented many problems. But some critics of Kant appear.
Herder opposes the Kantian dualism of mental faculties and urges the unity of the soul-life.
Thought and will, he maintained, spring from a common ground. The history of mankind is a process of evolution directed toward the ideal of humanity. Our rational capacity should therefore be educated and fashioned into reason, our more refined senses into art, our impulses into genuine freedom and beauty, our motives into the love of humanity. Jacobi declared that the Critique logically ends in subjective idealism, and rejected its conclusions. Jacob Fries seeks to combine the teachings of Kant and Jacobi.