He published works on Leibnitz, empiricism and scepticism in Hume's philosophy, modern pessimism, Kantic criticism, English philosophy, Heraclitus of Ephesus and many other subjects.
The first Greek writer, so far as we know, who does so is Heraclitus (c. 500 B.C.).
Heraclitus again deserves a prominent place in a history of the idea of evolution.
Heraclitus is in a real sense the founder of metaphysics.
To appreciate the significance of the doctrines of Heraclitus, it must be borne in mind that to Greek philosophy the sharp distinction between subject and object which pervades modern thought was foreign, a consideration which suggests the conclusion that, while it is a great mistake to reckon Heraclitus with the materialistic cosmologists of the Ionic schools, it is, on the other hand, going too far to treat his theory, with Hegel and Lassalle, as one of pure Panlogism.