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 PRINCIPLES OF THE SYSTEM. 91 tain knowledge which renders it self-evident and independ- ent of all proof, which makes us absolutely unable to doubt it? Its entire clearness and distinctness. Accordingly, I may- conclude that everything which I perceive as clearly and distinctly as the cogito ergo sum is also true, and I reach this general rule, omtie est verum, quod clare et distincte per- cipio. So far, then, we have gained three things : a challenge to be inscribed over the portals of certified knowledge, de omnibus dubitandum ; a basal truth, suvi cogitans ; a cri- terion of truth, clara et distincta perceptio. The doubt of Descartes is not the expression of a resigned spirit which renounces the unattainable ; it is precept, not doctrine, the starting point of philosophy, not its conclusion, a methodological instrument in the hand of a strong and confident longing for truth, which makes use of doubt to find the indubitable. It is not aimed at the possibility of attain- ing knowledge, but at the opinion that it has already been attained, at the credulity of the age, at its excessive ten- dency toward historical and poly-historical study, which confuses the acquisition and handing down of information with knowledge of the truth. That knowledge alone is certain which is self-attained and self-tested — and this cannot be learned or handed down ; it can only be redis- covered through examination and experience. Instead of taking one's own unsupported conjectures or the opinions of others as a guide, the secret of the search for truth is to become independent and of age, to think for one's self ; and the only remedy against the dangers of self-deception and the ease of repetition is to be found in doubting everything hitherto considered true. This is the meaning of the Cartesian doubt, which is more comprehensive and more thorough than the Baconian. Descartes disputed only the certitude of the knowledge previously attained, not the possibility of knowledge — for of the latter no man is more firmly convinced than he. He is a rationalist, not a skeptic. The intellect is assured against error just as soon as, freed from hindrances, it remains true to itself, as it puts forth all its powers and lets nothing pass for truth which is not clearly and distinctly known, Descartes demands the same thing for the human understanding as Rousseau at a later