Note 1: First published (two volumes) in Berlin, 1900–1. In 1914 the contents were recast and published in a different form as Die Rätsel der Philosophie (Riddles of Philosophy). The fourth edition is included in the Complete Edition of Rudolf Steiner's work. (Rudolf Steiner Nachlassverwaltung, Dornach, Switzerland.)

Note 2: “Unsere Welt ist das versinnlichte Material unserer Pflicht.” The rendering given is that of Professor Robert Adamson, in the series of Blackwood's Philosophical Classics for English readers. Alternative words for versinnlichte might be “sense-perceptible” or “tangible”. The quotation is from Fichte's work, Über den Grund unseres Glaubens an eine göttliche Weltregierung (1798).