I am not ignorant of what has been advanced against the certainty of the exact sciences, nor of the difficulties they present when called before the tribunal of metaphysics. In the first volume of _Protestantism compared with Catholicity_, I consecrated a chapter to what I call _instinct of faith_; and this instinct, I there maintained, also exercises its influence upon the exact sciences. These I do not place above moral sciences; I esteem these latter the more; but I must avoid an exaggeration that would destroy them all. CHAPTER XXXIV. SUMMARY AND CONCLUSION. 337. In concluding this book, I wish to give a summary of my views on certainty, wherein I shall show the connection between the doctrines exposed in the different chapters. When philosophy meets a necessary fact its duty is to accept it. Such a fact is certainty. To dispute its existence, is to dispute the splendor of the sun at mid-day. Mankind are certain of many things; philosophers, skeptics not excluded, are equally so. Absolute skepticism is impossible. Setting aside the question of certainty, philosophy is free from extravagance, and is established in the domain of reason; it can there examine how we acquire certainty, and upon what it is based. The human race is endowed with certainty as a quality annexed to life, a spontaneous result of the development of the soul's faculties. Certainty is natural; consequently it precedes all philosophy, and is independent of the opinions of men. For the same reason the question of certainty, although important to the knowledge of the laws to which our mind is subject, is, and always will be, unproductive of practical results. It is a dividing line fixed by reason lest at any time something should descend from the realm of abstraction prejudicial to society or individuals. Thus from its first investigations, philosophy forms a kind of alliance with good sense; they mutually promise never to be hostile to each other. When we examine the foundations of certainty a question arises upon the first principle of human cognitions: does it exist, and what is it? This question may have a double meaning. It may either mean a primitive truth containing all others, as the seed does plants and fruits; or simply a resting-point. The former gives rise to the question of transcendental science; the latter is the cause of the disputes in the schools on the preference of different truths in relation to the dignity of first principle. If truth exists, there must be means of knowing it, hence the question of the value of criteria.