Notes on Diogenes Laertius' life of Socrates

Diogenes Laertius is the author of the only work to survive from antiquity which describes the history of philosophy from its inception to the beginnings of the Common Era, called The Lives of the Philosophers. The latest philosopher he names is a student of Sextus Empiricus, which puts him in the middle of the 3rd century of the Common Era.

He collected a hodge-podge of material excerpted from other sources, which happens to have survived, unlike many other authors' works.

An example of argument using Diogenes Laertius
  1. On P. 334, Diogenes Laertius says that Socrates offered 25 drachmae as a fine at his trial, and then suggested free meals at the Prytaneum.
  2. He does not say where he got that information from, but at the beginning of the same paragraph, he says he derives his information from Justus of Tiberias.
  3. Thus it is not certain, but it is likely that Justus of Tiberias is the one who reports that Socrates proposed a 25 drachmae fine.
  4. On P. 334, Diogenes Laertius also says that Eubulides says that the fine Socrates offered was 100 drachmae.
  5. We know that Diogenes had read Plato's Apology.
  6. The Apology says that Socrates first suggested free meals, then a 1 mina fine.
  7. Diogenes Laertius does not mention the Apology version of the fine.
  8. A careful historian would have noticed the discrepancy.
  9. Our conclusion is that Diogenes Laertius was not a careful historian in this instance, because he neglected one of the sources available to him.
  10. Numbers are notorious for being inaccurate in ancient sources.
  11. Therefore, perhaps the discrepancy is only apparent: maybe our manuscripts are mistaken.
  12. It remains true that Diogenes does not cite Plato.
  13. It is also true that Plato has the reverse order of proposals: Plato says that the proposal of free meals came first, the fine second.
  14. The free meals are clearly and undboubtedly not an option which the jury would accept.
  15. They might accept a fine, even a small one.
  16. Therefore, which offer was made second, and stands as the actual proposal, is possibly important.
  17. Therefore even if the numbers are incorrect, Diogenes has still neglected a possibly important factor in one of the sources available to him.
  18. Justus of Tiberias was a Jewish historian of the 1st century of the Common Era (information I got from "Der neue Pauly").
  19. Eubulides was a Megarian philosopher from the middle of the 4th century before the Common Era (information I got from "Der neue Pauly").
  20. Thus both Justus of Tiberias and Eubulides came after Plato and did not know Socrates personally.
  21. Plato knew Socrates personally, and so was an eye-witness.
  22. Eye-witnesses are primary, and should be taken more seriously than others.
  23. Diogenes Laertius does not indicate that there is any difference between Plato and Xenophon and later sources such as Justus of Tiberias and Eubulides.
  24. Therefore, what?

Our conclusion should be limited logically to this particular instance, but we should be inclined not to trust DIogenes Laertius blindly, but it raises a broader question: How can we decide what to trust of what Diogenes Laertius says?