Tablet to Dr. Forel

In this tablet which is considered ʻAbdu'l-Bahá's last significant philosophical work; ʻAbdu'l-Bahá discusses the differences between the mineral, vegetable, animal and human worlds, the spiritual nature of man and proofs of the existence of God. It also expounds the logical necessity of the existence of the mind, and the relationship between the faculties of the mind and the human soul.

This letter was used as a model by William S. Hatcher (1935–2005) in his 1994 article entitled "A Scientific Proof of the Existence of God", first published in Russian in March 1992 under the title: "Научное доказательство существования бога".