Off and on for the last several years, I have searched and searched in Plato for a quote, culminating in pretty much an all day search today as I'm dotting the jots and crossing the tittles of my philosophy book before publication.
At the beginning of the chapter on Socrates in Sophie's World, Gaarder says that Socrates said, "He who knows what good is will do good." The heading of the section is, "The Right Insight Leads to the Right Action." Of course it's a bunch of bunk--humans are irrational animals far more than rational, in my estimation. But it's a key perspective and an idea a college graduate should have heard of so that they can later forget it.
Well I've done numerous Google searches. I can find these quotes on the web (especially in online study notes over Sophie's World). I even did a Google search in German thinking that some meticulous German would reference the quote. I did indeed find, "Wer weiss, was richtig ist, wird auch das Richtige tun." What I didn't find was a reference.
I did a number of Google searches on the complete works of Plato (who of course is the source for such Socrates quotes). "know good do good" "knowledge" "good" "virtue" "ignorance" ... I looked through the index of my own hardback collection of Plato's complete works.
Indeed, I found several stressed out students (both in English and German) trying to track down this quote, which is the main reason I am making this post... for posterity and the future desperate. And of course inviting thereby some elusive spirit from the ether who might disprove my conclusion.
My conclusion is that Socrates didn't give us a nice quote. These are all fair expressions of what he thought, but he wasn't particularly good at sound bites on this occasion. Here are some statements that come close:
1. "The man who has learned anything becomes in each case such as his knowledge makes him" (Gorgias 460b).
2. "No one voluntarily does wrong, but all who do wrong do so against their own will" (Gorgias 509e, but this is a question-the idea is that if a person truly knows what good is, he or she does it)
3. "Virtue is knowledge" (Meno 87c). This is what I'm going with. The title of my post is a paraphrase, "To know the good is to do the good." The problem is that at this point in the Meno, it is still a matter of debate and it isn't really Socrates' main point. Socrates does believe that knowledge is a guide to right action, but he doesn't believe it is the only guide. His final point is that virtue is ultimately a matter of divine inspiration--the gods give the knowledge or even right opinion that results in virtue.
4. "I never wrong anyone intentionally" (Apology 37a). Again, what is hiding behind this statement is Socrates' belief that all wrongdoing is based on ignorance because knowledge can only lead to right action.
So there you have it. Unless someone corrects me from the ether, there is no silver bullet on a quote here. Yes, this was Socrates' perspective. But he did not give us a nice, crisp quote to tweet.