Fichte's philosophy was pivotal in the development of nineteenth-century German idealism from Kant's critical philosophy. Fichte believed that Kant had posed the one fundamental question of philosophy: how is our experience of the world, as spatio-temporal and law-governed, possible? The answer he works out here is one of the most uncomprimising forms of philosophical idealism. The isolated absolute self is presented as the sole source from which the forms of human knowledge can be dialectically deduced. In the 1974 version of Wissenschaftslehre is Fichte's best known philosophical work; and the two Introductions which Fichte added later throw a helpful light on the system. This, the only modern and reliable translation, was first published in America in 1970, and is now made available again, with corrections, for all those with an interest in Fichte and in German Idealism.