The philosophy of Mansel, like that of Sir William Hamilton, was mainly due to Aristotle, Immanuel Kant and Thomas Reid. Like Hamilton, Mansel maintained the purely formal character of logic, the duality of consciousness as testifying to both self and the external world, and the limitation of knowledge to the finite and "conditioned." His doctrines were developed in his edition of Aldrich's Artis logicae rudimenta (1849) – his chief contribution to the reviving study of Aristotle – and in his Prolegomena logica: an Inquiry into the Psychological Character of Logical Processes (1851, 2nd ed. enlarged 1860), in which the limits of logic as the "science of formal thinking" are rigorously determined.[2]
In his Bampton lectures on The Limits of Religious Thought (1858, 5th ed. 1867; Danish trans. 1888) he applied to Christiantheology the metaphysical agnosticism which seemed to result from Kant's criticism, and which had been developed in Hamilton's Philosophy of the Unconditioned. While denying all knowledge of the supersensuous, Mansel deviated from Kant in contending that cognition of the ego as it really belongs among the facts of experience. Consciousness, he held – agreeing thus with the doctrine of "natural realism" which Hamilton developed from Reid – implies knowledge both of self and of the external world. The latter Mansel's psychology reduces to consciousness of our organism as extended; with the former is given consciousness of free will and moral obligation.[2]
These lectures led Mansel to a bitter controversy with the Christian socialist theologian Frederick Maurice.[3]
A summary of Mansel's philosophy is contained in his article "Metaphysics" in the 5th edition of the Encyclopædia Britannica (1860). He also wrote
"Metaphysics or the Philosophy of Consciousness Phenomenal and Real" (4th ed., 1883), 408pps, Edinburgh, Adam and Charles Black
The Philosophy of the Conditioned (1866) in reply to John Stuart Mill's criticism of Hamilton;
Letters, Lectures, and Reviews (ed. Chandler, 1873),