- [http://archive.org/details/surdofmetaphysic00caru The surd of metaphysics; an inquiry into the question: Are there things-in-themselves? (1903) Paul Carus, 1852–1919 Retrieved May 18, 2012
- Stanford Encyclopedia of Philosophy on Kant's metaphysics.
- Glossary of Kant's technical terms by Stephen Palmquist
- Article from undergraduate journal Noesis
- Lecture notes by G.J Mattey
- Kant's System of Perspectives (Lanham: University Press of America, 1993) by Stephen Palmquist