[EP2:534] Four days after this lecture (Lowell 1), an anonymous listener sent Peirce the following question: "If not inconvenient for you, will you be kind enough to give tonight a summary- however brief- of your answer to the question 'What makes a Reasoning Sound?'" Peirce prepared a response that he read at the beginning of the third lecture. This response, found in MS 465, is as follows:
My first duty this evening is to reply to a note which asks me to give an explanation at my last lecture. The letter did not come to hand until the following morning. The question asked is what my answer in the first lecture was to the question "What makes a Reasoning to be sound?" I had no intention of answering that question in my first lecture, because I dislike to put forth opinions until I am ready to prove them; and I had enough to do in the first lecture to show what does not make reasoning to be sound. Besides in this short course it seems better to skip such purely theoretical questions. Yet since I am asked, I have no objection to saying that in my opinion what makes a reasoning sound is the real law that the general method which that reasoning more or less consciously pursues does tend toward the truth. The very essence of an argument,- that which distinguishes it from all other kinds of signs,- is that it professes to be the representative of a general method of procedure tending toward the truth. To say that this method tends toward the true is to say that it is a real law that existences will follow. Now if that profession is true, and the conclusions of that method really will be true, to the extent and in the manner in which the argument pretends that they will, the argument is sound; if not, it is a false pretension and is unsound. I thus make the soundness of argument to consist in the facts of the case and not at all in whether the reasoner feels confidence in the argument or not. I may further say that there are three great classes of argument, Deductions, Inductions, and Abductions; and these profess to tend toward the truth in very different senses, as we shall see. I suppose this answers the question intended. However, it is possible that my correspondent did not intend to ask in what I think the soundness of reasoning consists, but by the question "What makes reasoning sound?" he may mean "What causes men to reason right?" That question I did substantially answer in my first lecture. Namely, to begin with, when a boy or girl first begins to criticize his inferences, and until he does that he does not reason, he finds that he has already strong prejudices in favor of certain ways of arguing. Those prejudices, whether they be inherited or acquired, were first formed under the influence of the environing world, so that it is not surprising that they are largely right or nearly right. He, thus, has a basis to go upon. But if he has the habit of calling himself to account for his reasonings, as all of us do more or less, he will gradually come to reason much better; and this comes about through his criticism, in the light of experience, of all the factors that have entered into reasonings that were performed shortly before the criticism. Occasionally, he goes back to the criticism of habits of reasoning which have governed him for many years. That is my answer to the second question. http://gnusystems.ca/Lowells.htm }{ Peirce's Lowell Lectures of 1903
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