First, as to fallibility and infallibility. It is very common, doubtless, especially in religious controversy, to confuse infallibility with certitude, and to argue that, since we have not the one, we have not the other, for that no one can claim to be certain on any point, who is not infallible about all; but the two words stand for things quite distinct from each other. For example, I remember for certain what I did yesterday, but still my memory is not infallible; I am quite clear that two and two makes four, but I often make mistakes in long addition sums. I have no doubt whatever that John or Richard is my true friend, but I have before now trusted those who failed me, and I may do so again before I die. A certitude is directed to this or that particular proposition; it is not a faculty or gift, but a disposition of mind relatively to a definite case which is before me. Infallibility, on the contrary, is just that which certitude is not; it is a faculty or gift, and relates, not to some one truth in particular, but to all possible propositions in a given subject-matter. We ought in strict propriety, to speak, not of infallible acts, but of acts of infallibility. A belief or opinion as little admits of being called infallible, as a deed can correctly be called immortal. A deed is done and over; it may be great, momentous, effective, anything but immortal; it is its fame, it is the work which it brings to pass, which is immortal, not the deed itself. And as a deed is good or bad, but never immortal, so a belief, opinion, or certitude is true or false, but never infallible. We cannot speak of things which exist or things which once were, as if they were something _in posse_. It is persons and rules that are infallible, not what is brought out into act, or committed to paper. A man is infallible, whose words are always true; a rule is infallible, if it is unerring in all its possible applications. An infallible authority is certain in every particular case that may arise; but a man who is certain in some one definite case, is not on that account infallible.