Now what is an “infallible means”? It is a means of coming at a fact without the chance of mistake. It is a proof which is sufficient for certitude in the particular case, or a proof that is certain. When then Chillingworth says that there can be no “rational assent to the Church’s infallibility” without “some infallible means of knowing that she is infallible,” he means nothing else than some means which is certain; he says that for a rational assent to infallibility there must be an absolutely valid or certain proof. This is intelligible; but observe how his argument will run, if worded according to this interpretation: “The doctrine of the Church’s infallibility requires a proof that is certain; and that certain proof requires another previous certain proof, and that again another, and so on _ad infinitum_, unless indeed we dig so deep as to settle all upon something evident of itself.” What is this but to say that nothing in this world is certain but what is self-evident? that nothing can be absolutely proved? Can he really mean this? What then becomes of physical truth? of the discoveries in optics, chemistry, and electricity, or of the science of motion? Intuition by itself will carry us but a little way into that circle of knowledge which is the boast of the present age. I can believe then in the infallible Church without my own personal infallibility. Certitude is at most nothing more than infallibility _pro hac vice_, and promises nothing as to the truth of any proposition beside its own. That I am certain of this proposition to-day, is no ground for thinking that I shall have a right to be certain of that proposition to-morrow; and that I am wrong in my convictions about to-day’s proposition, does not hinder my having a true conviction, a genuine certitude, about to-morrow’s proposition. If indeed I claimed to be infallible, one failure would shiver my claim to pieces; but I may claim to be certain of the truth to which I have already attained, though I should arrive at no new truths in addition as long as I live. 2.