ing the inconsistent and premature metaphysical conceptions which stealthily creep into all branches of knowledge. The natural scientist frequently rails against metaphysics in the very words of metaphysics, without knowing that his entire mental activity is based on metaphysical preconditions. Metaphysics is the old man of the sea whom the scientific Sindbad carries on his own shoulders, without, however, feeling the load.
After having studied the limits and validity of human knowledge, the philosopher is ready for the construction of his metaphysical system. He calls to his aid the history of philosophy, which unrolls before him the thoughts of past ages and bids him profit by their experience. The history of philosophy must not be regarded as 'a disconnected succession of arbitrary individual opinions and clever guesses,' it is not a formless aggregate of errors, not a series of unsuccessful attempts to reach truth. It is not a Sisyphean labor, a Penelopean woof. The history of philosophy is a development, an evolution, in which the forms which follow generally show an advance over what precedes. And even if it were a mere catalogue of errors, it would be of service to the metaphysician by pointing out to him the lines of thought that have ended in blind alleys; it would warn him against wasting his energies in fields that have been worked over. The man who knows how a solution can not be effected is on the road to knowledge.