I then set myself earnestly to examine the notions we derive from the evidence of the senses and from sight in order to see if they could be called in question. The result of a careful examination was that my confidence in them was shaken. Our sight for instance, perhaps the best practised of all our senses, observes a shadow, and finding it apparently stationary pronounces it devoid of movement. Observation and experience, however, show subsequently that a shadow moves not suddenly, it is true, but gradually and imperceptibly, so that it is never really motionless. Again, the eye sees a star and believes it as large as a piece of gold, but mathematical calculations prove, on the contrary, that it is larger than the earth. These notions, and all others which the senses declare true, are subsequently contradicted and convicted of falsity in an irrefragable manner by the verdict of reason. Then I reflected in myself: “Since I cannot trust to the evidence of my senses, I must rely only on intellectual notions based on fundamental principles, such as the following axioms: ‘Ten is more than three. Affirmation and negation cannot coexist together. A thing cannot both be created and also existent from eternity, living and annihilated simultaneously, at once necessary and impossible.’” To this the notions I derived from my senses made the following objections: “Who can guarantee you that you can trust to the evidence of reason more than to that of the senses? You believed in our testimony till it was contradicted by the verdict of reason, otherwise you would have continued to believe it to this day. Well, perhaps, there is above reason another judge who, if he appeared, would convict reason of falsehood, just as reason has confuted us. And if such a third arbiter is not yet apparent, it does not follow that he does not exist.” To this argument I remained some time without reply; a reflection drawn from the phenomena of sleep deepened my doubt. “Do you not see,” I reflected, “that while asleep you assume your dreams to be indisputably real? Once awake, you recognise them for what they are—baseless chimeras. Who can assure you, then, of the reliability of notions which, when awake, you derive from the senses and from reason? In relation to your present state they may be real; but it is possible also that you may enter upon another state of being which will bear the same relation to your present state as this does to your condition when asleep. In that new sphere you will recognise that the conclusions of reason are only chimeras.”