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 (you can verify this yourself by searching for "Socrates").
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
therefore
Socrates is mortal ;
...
You can verify 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. This makes sense; this book was extremely popular in its time (for its kind of work), as witnessed by its many editions.
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.
Sextus Empiricus (c. 160 - c. 210 AD) made a different but somewhat similar statement in Outlines of Pyrrhonism (Pyrrhōneioi hypotypōseis) (formatting is my own):
Note: It was tricky to verify that this proof of "Socrates is an animal" was in the work of Sextus Empiricus. On 2016-05-25 Mauro ALLEGRANZA reported on the Philosophy Stack Exchange that this text was in Outlines of Scepticism (Pyrrhōneioi hypotypōseis), Book II, 164. However, in the process of trying to verify statement, I found there was a citation error. The Greek title is fine, but the given translated English title is incorrect. The English translation is actually Outlines of Pyrrhonism, not Outlines of Scepticism. Verifying the citation was made harder because the link originally provided didn't work for me. That said, this citation was enough of a clue for me to eventually track down the correct citation. Once I realized that I should start with the Greek title (not the incorrect English translation), I successfully tracked down an English translation to verify the claim. Specifically I found Sextus Empiricus: Outlines of Pyrrhonism, Volume 273; Volume 291; Volume 311; Volume 382 of the Loeb classical library Greek authors. The author is Sextus Empiricus, of course. The translation I used was translated by Robert Gregg Bury, published by W. Heinemann, 1933, with ISBN 0434992739 and ISBN 9780434992737. Once I found the correct title, and searched this English translation available online, I found the claimed text on page 257 of this translation. So my thanks to Mauro ALLEGRANZA for helping me find this source. Hopefully I have finished the job of correcting and verifying the citation.
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.
It's worth noting that "man" in this context doesn't mean "male" but simply "human". As evidence, I point to Bertrand Russell's "On Denoting" (in Mind, 1905). This article clearly shows that the phrase "All men are mortals" was interpreted as "if x is human, [then] x is mortal is always true".
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.
(C) Copyright David A. Wheeler. Released under Creative Commons Attribution-ShareAlike version 3.0 or later (CC-BY-SA-3.0+).