How does man acquire this certainty? He knows not: he had it before reflecting on it; he is astounded to hear it made a matter of dispute, and he might never have suspected it could be asked, why we are certain that what affects our senses exists. It is of no use to ask him how he made so precious an acquisition; he regards it as a fact scarcely distinct from his own existence. He has no recollection of the order of sensations in his infancy; he finds his mind now developed, but is as ignorant of the laws of its development as he is of those which presided over the generation and growth of his body. 7. Philosophy should begin by explaining, not by disputing the fact of certainty. If we are certain of nothing, it is absolutely impossible for us to advance a single step in any science, or to take any part whatever in the affairs of life. A thorough-going skeptic would be insane, and that too with insanity of the highest grade. To such a one, all communication with other men, all succession of external actions, all thoughts, and even acts of the will would be impossible. Let us, then, admit the fact, and not be so extravagant as to say that madness sits on the threshold of philosophy. It is the part of philosophy to analyze, not to destroy its object; for by destroying its object it destroys itself. Every argument must have a resting-point, which must be a fact. Whether it be internal or external, idea or object, the fact must exist: we must begin by supposing something, and this something we call a fact. Whoever begins by denying or doubting all facts, is like the anatomist, who, before dissecting a corpse, burns it, and casts its ashes to the wind. 8. Philosophy then, it may be said, commences not with an examination, but with an affirmation. Granted, and this is a truth whose admission closes the door on much sophistry, and sheds a brilliant light over the whole theory of certainty. Philosophers are deceived when they imagine that they begin by doubting. Nothing is more false; when they think, they affirm, if nothing else, at least their own doubt: whenever they reason, they assert the connection of ideas, that is, the whole logical world.