German philosophy
Neo-Kantianism refers broadly to the revival of the type of philosophy explained by Immanuel Kant and of the interpretations of Kant provided by post-Kantian philosophers such as Schopenhauer, Jakob Friedrich Fries and Johann Friedrich Herbart. Major figures in the neo-Kantian movement, which began around the 1860s, include Friedrich Albert Lange and Hermann Cohen.
Critique of Pure Reason
Kant decided to find an answer and spent at least twelve years thinking about the subject. Although the "Critique of Pure Reason" was set down in written form in just four to five months, while Kant was also lecturing and teaching, the work is a summation of the development of Kant's philosophy throughout that twelve-year period.