Brief entry from the Internet Encyclopedia of Philosophy on this German writer.

Detailed study of this thinker by George di Giovanni, from the Stanford Encyclopedia of Philosophy.

Note on this writer's influence on New England Transcendentalism, including a lengthy passage from Octavius Brooks Frothingham.

Paragraph on this religious thinker from the 2001 Columbia Encyclopedia.

Wikipedia entry, drawing on the 1911 Encyclopaedia Britannica.