‘By our senses and our memory, by testimony and other means, we have the certain knowledge of many truths which we do not perceive to be necessary; their contraries therefore may be possible for aught we know. But we know that whatever is true, whether necessary or not, is possible. Our knowledge therefore of what is possible keeps pace with our knowledge of truth, whether contingent or necessary. Beyond this, I am afraid our knowledge of what is possible is conjectural. And although we are apt to think everything to be possible which we do not perceive to be impossible, yet in this we may be greatly deceived. You know well, sir, that mathematics affords many instances of impossibilities _in the nature of things_, which no man would have dreamed of or believed, until they were discovered by accurate and subtle reasoning. Perhaps if we were able to reason demonstratively to as great an extent in other subjects as in mathematics, we might discover many things to be impossible which we now take to be possible. We are apt to think it possible that God might have made an universe of sensible and rational creatures, into which neither natural nor moral Evil should ever enter. It may be so for what I know. But how are you certain that this is possible? I can distinctly conceive it, say you; therefore it is possible. I do not admit this argument. May not a man who is a mathematician as distinctly conceive that in the infinite variety of numbers gradually ascending, there is no ratio whatsoever which is not equal to the ratio of some one whole number to some other whole number? Yet the mathematician can demonstrate that there are innumerable ratios which are not equal to the ratio of some one number to another. Many mathematicians, taking it for granted that it was possible to square the circle, have spent their lives in a fruitless pursuit. May not our taking things to be possible, in matters of higher moment, when we can show no good reason that they are so, lead us into unnecessary disputes and vain theories? Ought we to admit that as a just argument in reasoning, or even as a pressing difficulty, which is grounded on the supposition that such a thing is possible, when in reality we have no good evidence of its being possible, and for anything we can show to the contrary, it may be impossible?’