 I do not believe you doubt that [that we can learn science, with great contentment] because you experience this every day in yourself, and if you doubt it I ask whether you know that you are doubting; if you know it, you must know something, and consequently you do not doubt everything; an if you doubt that you doubted, I shall force you to admit infinite regress, which you say you reject, so that wherever you go, you must confess that there is some truth, and consequently you must say farewell to your Pyrrhonism. (VS I: 204)