German Idealism
Background
Immanuel Kant bridged the two dominant philosophical schools in the 18th century:
1) Empiricism - knowledge attained through the senses alone a posteriori (after experience),
2) Rationalism - knowledge could be attained by reason alone a priori (before to experience).

The solution Kant proposed was that certain knowledge transcends sensory evidence a priori known as ‘transcendental idealism’.  The philosophical meaning of idealism is that the properties we discover in objects depend on the way we perceive them, not on something they possess ‘in-themselves’.

The period after Kant is known as post-Kantian idealism or post-Kantianism of which subsequent strains became German idealism where the idealism is a monistic idealism. The two broad categories of the German idealist thinkers:
 1) Transcendental: Kant, Fichte
 2) Absolute: Schelling, Hegel

The Creative Self
Continental Rationalism moved on to German idealism which was a reaction against Kant's Critique of Pure Reason (CPR) and to mechanistic science.  An organic model with a focus on a priori knowledge that emphasized the creative Self - the inner intellectual resources and rationality of the Self. It was closely linked with both Romanticism and the revolutionary politics of the Enlightenment.  And it was a continuation of Kant’s Copernican Revolution – the subject, rather than the object, is central to knowledge.

Structure of Consciousness

The late professor of philosophy Dr. Arthur Holmes (Wheaton college) sheds some clarifying thoughts on German Idealism:
“We've observed during the modern period from Descartes to culminating in Kant the ongoing question about the nature of the self. What am I?
Descartes says, "A thinking thing!"  Locke isn't so sure. Hume finds only a bundle of perceptions with nothing to unify. Kant finds that there is this synthetic unity of our perceptions (functional unity). Whereby there is some sort of unification of the field of consciousness. It is the structure of consciousness that is the unifier.
That is the point of departure for the German Idealist. They are not looking for some 'mind substance' or 'soul substance' in the Cartesian sense. They are not looking for immortal souls in the Platonic sense that have some eternal preexistence. What the German Idealist are trying to understand is the Self as structured consciousness.  What is the unifying action of the Self? You get different answers. Functional unities.
 1) Fichte: moral consciousness. Takes off from Kant's Critique of Practice Reason.
 2) Schelling: what Kant calls the teleological in the Critique of Judgment - the Aesthetic consciousness. Schelling is the major philosopher of German Romanticism.
 3) Hegel: simply says no; it's this conceptual capacity that we have. The ongoing process of trying to graph the concept of being.  You have to distinguish the finite self (unity of the self) and the Absolute Self (monistic). Absolute in the sense of the one all inclusive 'ground of being'.