He also found time for philosophical speculations, and in 1830 he published his "Inquiries concerning the Intellectual Powers of Man and the Investigation of Truth", which was followed in 1833 by a sequel, "The Philosophy of the Moral Feelings".
* «Исследования об умственных способностях человека и об изыскании истины» (Inquiries concerning the Intellectual Powers of Man and the Investigation of Truth, 1830);* «Философия нравственных чувств» (The Philosophy of the Moral Feelings, 1833).