Many books and articles use this as a standard example of logic:
The question is: where did this example come from?
Some people think this example comes from Aristotle, but Aristotle did not say anything like this example. Aristotle created the field of logic, because he was the first person to study and write about logic independent of any particular argument. So it is true that he discussed this form of argument. But there is no evidence that Aristotle wrote this particular example. Just look at Aristotle Organon And Other Works by Aristotle (translated under the editorship of W.D. Ross), which includes the six books collectively called the Organon as well as Rhetoric. Aristotle mentions Socrates often, as well as the terms mortal and immortal, but he never uses them exactly this way.
The earliest document I can find with this specific example is from 1843, specifically A System of Logic: Ratiocinative and Inductive, Presenting a Connected View of the Principles of Evidence and the Methods of Scientific Investigation by John Stuart Mill, 1843 (first edition), Book II Chapter 3 page 245. On that page we see:
When we say,
All men are mortal
Socrates is a man
Socrates is mortal ;
You can verifiy this via Logic Museum or the Internet Archive.
Mill's A System of Logic... went through a large number of revisions over many years. For example, its 8th edition was released in 1872. Unsurprisingly, these revisions moved material around, For example, the 3rd edition was published in 1851, and it first mentions the "Socrates is a man" example in Book II, Chapter II, Of Ratiocination, or Syllogism, p. 190. A discussion of Mill's writing of the original first edition, and the changes it went through afterward, is contained in The Collected Works of John Stuart Mill, Volume VII - A System of Logic Part I. Since we are focused on its first use, and its first edition includes the example, that appears to be its first full use.
If you find an earlier example, please let me know.
As I already noted, Aristotle created the field of logic, because he was the first person to study and write about logic independent of any particular argument. You can see many of his works in Aristotle Organon And Other Works by Aristotle (translated under the editorship of W.D. Ross). But nothing exactly like this is said.
On 2016-05-25 Mauro ALLEGRANZA reported on the Philosophy Stack Exchange that Sextus Empiricus (c. 160 - c. 210 CE) made a somewhat similar statement in Outlines of Scepticism (Pyrrhōneioi hypotypōseis), Book II, 164 (I need to verify this):
The Love of Wisdom: An Introduction to Philosophy for Theologians by Andrew Davison (2013) page 48 discusses Aristotle’s works, and says that “Perhaps the most famous example is the following” with this example. However, note that its wording does not imply that Aristotle directly said this example.
"How Aristotle Created the Computer" by Chris Dixon (The Atlantic, 2017-03-20) says, "Aristotle’s central observation was that arguments were valid or not based on their logical structure, independent of the non-logical words involved. The most famous argument schema he discussed is known as the syllogism..." followed by that statement. This text could be easily interpreted as claiming that Aristotle actually used this example, but it doesn't exactly say that either. It's true that Aristotle emphasized logical structure, and if that was the intent it's correct.
This example was first published in 1843 in A System of Logic: Ratiocinative and Inductive, Presenting a Connected View of the Principles of Evidence and the Methods of Scientific Investigation by John Stuart Mill.
Feel free to see my home page at https://dwheeler.com. You may also want to look at my paper Why OSS/FS? Look at the Numbers! and my book on how to develop secure programs.
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