The fact is that any attempt to prove the truth of our faculties must necessarily fail. Did we set ourselves to the task of proving by argument or by authority that we are not wrong in believing in our own existence or that of an external world, or did we attempt to establish the trustworthiness of our faculties by resolving it into the veracity of God, our effort must needs be as abortive as it is superfluous, since it involves the necessity not only of proving the fact, but of _proving the proof itself_, and that, too, by the aid of the very faculties whose trustworthiness is in question! There are certain ultimate facts beyond which it is impossible to push our speculative inquiries; certain first or fundamental principles of Reason, which are in themselves indemonstrable, but which constitute the ground or condition of all demonstration; certain intuitive perceptions, which are widely different from rational deductions, but which determine and govern every process of reasoning and every form of belief. To deny the _certainty_ of our intuitive perceptions, merely because we cannot prove by argument the truth of our mental faculties, would virtually amount to a rejection of all evidence except such as comes to us only through _one_ channel, and _that_ the circuitous one of a process of reasoning; while, by the constitution of our nature, we are qualified and privileged to draw it fresh, in many cases, at its spring and fountain-head. It may be as impossible for man to prove the trustworthiness of his intellectual faculties as it is for the bee to prove the truth of its marvellous instinct; but, in either case, the reason may be that any such proof is unnecessary, that it is superseded by the laws of Instinct in the one, and by the laws of Thought in the other, and that by these laws a better and surer provision is made for our guidance than any that could have been found in a mere logical faculty,--a natural and irresistible authority, which the Skeptic may dispute, but cannot destroy, and which, however disowned in theory, must be practically obeyed.