Lotze's first essay was his dissertation _De futurae biologiae principibus philosophicis_, with which he gained (1838) the degree of doctor of medicine, after having only four months previously got the degree of doctor of philosophy. Then, secondly, there arose the question whether the methods of exact science sufficed to explain the connexion of phenomena, or whether for the explanation of this the thinking mind was forced to resort to some hypothesis not immediately verifiable by observation, but dictated by higher aspirations and interests. And, if to satisfy these we were forced to maintain the existence of a world of moral standards, it was, thirdly, necessary to form some opinion as to the relation of these moral standards of value to the forms and facts of phenomenal existence. These different tasks, which philosophy had to fulfil, mark pretty accurately the aims of Lotze's writings, and the order in which they were published. He laid the foundation of his philosophical system very early in his _Metaphysik_ (Leipzig, 1841) and his _Logik_ (1843), short books published while he was still a junior lecturer at Leipzig, from which university he migrated to Göttingen, succeeding Herbart in the chair of philosophy. But it was only during the last decade of his life that he ventured, with much hesitation, to present his ideas in a systematic and final form. The two books mentioned remained unnoticed by the reading public, and Lotze first became known to a larger circle through a series of works which aimed at establishing in the study of the physical and mental phenomena of the human organism in its normal and diseased states the same general principles which had been adopted in the investigation of inorganic phenomena. These works were his _Allgemeine Pathologie und Therapie als mechanische Naturwissenschaften_ (Leipzig, 1842, 2nd ed., 1848), the articles "Lebenskraft" (1843) and "Seele und Seelenleben" (1846) in Rud. Wagner's _Handwörterbuch der Physiologie_, his _Allgemeine Physiologie des Körperlichen Lebens_ (Leipzig, 1851), and his _Medizinische Psychologie oder Physiologie der Seele_ (Leipzig, 1852).