Error as negativity; impossibility of a special treatment of errors--Positive and existing errors--Positive errors as practical acts--Practical acts and not practical errors--Economically practical acts, not morally practical acts--Doctrine of error, and doctrine of necessary forms of error--Logical nature of all theoretical errors--History of errors and phenomenology of error--Deduction of the forms of logical errors. Forms deduced from the concept of the concept, and forms deduced from the other concepts--Errors derived from errors--Professionally and nationality of errors. II ÆSTHETICISM, EMPIRICISM AND MATHEMATICISM Definition of these forms--Æstheticism--Empiricism--Positivism, the philosophy founded upon the sciences, inductive metaphysic--Empiricism and facts--Bankruptcy of Empiricism: dualism, agnosticism, spiritualism and superstition--Evolutionistic positivism and rationalistic positivism--Mathematicism--Symbolical mathematics--Mathematics as a form of demonstration of philosophy--Errors of mathematical philosophy--Dualism, agnosticism and superstition of mathematicism. III THE PHILOSOPHISM Rupture of the unity of the _a priori_ synthesis--Philosophism, logicism or panlogicism--Philosophy of history--Contradictions in its assumptions--Philosophy of history and false analogies--Distinction between Philosophy of history and books so entitled--Merits of these, philosophic and historical--Philosophy of nature--Its substantial identity with Philosophy of history--Contradictions of Philosophy of nature--Books entitled Philosophy of nature--Contemporary seekings for a Philosophy of nature and their various meanings. IV THE MYTHOLOGISM Rupture of the unity of the _a priori_ synthesis. The mythologism --Essence of myth--Problems relating to theory of myth--Myth and religion--Identity of the two spiritual forms--Religion and philosophy--Conversion of errors, the one into the other--Conversion of the mythologism into philosophism (theology) and of the philosophism into the mythologism (mythology of nature, historical apocalypses, etc.)--Scepsis. DUALISM, SCEPTICISM AND MYSTICISM Dualism--Scepsis and scepticism--Mystery--Critique of affirmations of mystery in philosophy--Agnosticism as a particular form of scepticism--Mysticism--Errors in other parts of philosophy--Conversion of these errors into one another and into logical errors. VI THE ORDER OF ERRORS AND THE SEARCH FOR TRUTH