 Condillac’s other philosophical works support and embellish the doctrines of the Essay and the Treatise. They are the Treatise on Systems of 1749, which is devoted to critiquing the metaphysics and the methodology of earlier philosophers, the Treatise on Animals of 1755, which attempts to explain how human souls differ from those of animals with respect to intelligence and free will, the “Dissertation on Liberty”, an important short work appended to the Treatise on Sensations that further addresses the issue of human free will, the “Summary [extrait raisonné] of the Treatise on Sensations,” originally included in the Treatise on Animals, and a textbook on Logic (1780). He also published a work on commerce and government, assembled a dictionary of synonyms, and put together a multi-volume course of studies that he had developed while tutoring the Prince of Parma. The latter dealt principally with history but also included some philosophical material, including a different presentation of logic. At the time of his death he left an incomplete a work entitled The Language of Calculation.