In their defense, most of who had to scour our brains for a quotation relating to Socrates would probably come up with "Know thyself", and would have to make a conscious effort to say "yourself."
As djacobs also pointed out, "Know thyself" is likely a more faithful translation than "Know yourself." Thy is the familiar form of "your."
It passed out of favor after Cromwell's Commonwealth. Under the puritans, everyone was all thee and thou to each other, under the belief that we were all 'family' in Christ, and distancing yourself by using the formal 'your' was unchristian. Then after the commonwealth fell the pendulum swung the other way and people stopped using it altogether.
But in any case, I'd imagine Socrates was in fact using it, so that is likely the best translation into English, even if it sounds archaic.
"Your" is the familiar form of "your" in the major English dialects spoken today, and there's no good reason to use a different one. Socrates did say it a long time ago, and "thy" has a long-ago flavor, but evoking the world of Shakespearean England (or modern-day pockets of Scotland) does not provide helpful context for a quote from Greece 2500 years ago.
Try using "thou" in an intimate situation, and your partner will be waiting for a Holy Grail punchline....
But seriously, "thou" just doesn't exist in modern English for the vast majority of English speakers on the planet. They use "thou" when they're quoting or reciting older texts, or when they want to make something new sound like something old. For instance, someone writing a prayer might sprinkle it with "thee" and "thou" to mimic the prayers and scriptures he's familiar with, because it puts him in a religious frame of mind. People who do that kind of thing tend to be inconsistent (just like when people use mock-archaic language for comedic purposes) and their usage would probably defy grammatical description.
"You" is both intimate and formal today for native English speakers. There is no distinction between the two cases.
For the Greeks and Early Modern English and really everyone except "modern" native English speakers, there is a distinction between the two, and "thou" is the closest translation we have. Much as you might not like it, it is not incorrect to translate another language's intimate second-person pronoun into English as "thou" because, in fact, that is the closest approximation we have.
Or, if you prefer, we could start saying "You-familiar should know you-familiar's self."
There's no graceful way to make the distinction in modern English, and the distinction isn't important to the phrase being translated. Why go out of your way to preserve it, to the extent of using awkward or archaic language?
"Know yourself" doesn't have the ring of authority and solemnity that "Know thyself" does, but when you think about why "Know thyself" sounds that way to an English speaker, it doesn't make any sense at all to exploit that connotation. (That is, unless Socrates himself would have approved of exploiting religiously tinged language to bypass rational skepticism. That doesn't sound like the Socrates I've heard about, but I must confess that I know Socrates mostly by reputation.)
Different languages make many different distinctions, and translations are inevitably lossy. Translation would be an impossible job if translators didn't feel free to drop distinctions that, in their view, aren't essential to the meaning of the text.
For example, in a Spanish news article about a criminal's appearance in court, the gender of the criminal's lawyer might be evident, but if the lawyer is not mentioned by name, the lawyer's gender would probably not be evident in the English translation. There's nothing wrong with that, unless there happens to be some special reason why the lawyer's gender is relevant to the story.
It depends on the goal of the translation. If the goal is accuracy, the difference between thou and you could be very important. (Disclaimer: IANA Ancient Greek translator.)
I agree with your sentiment but it may well be that his Greek quotation (being written in a far more intricate language than English) indicates this conjugation and pronoun.
for example, thou/thee/thine/thy are the singular informal english pronouns. although it is usually the case that informal pronouns get translated into formal when going from another language into english because they've fallen out of use, this is still a technically correct translation.
"Simply seeing pictures of tempting food can light up the pleasure-seeking areas of obese peoples' brains."
It's important not to infer causation from correlation. We can't assume that obese people can't stop eating because of this kind of reaction in the brain.
I'm sure if you showed a pothead weed, an alcoholic gin, or a cokehead coke then you'd see parts of their brain light up, because that is how their habits have been built, but this activity could be the result of long term bad habits as much as the cause of such habits.
"It's possible that these changes reflect how the brain has adapted to eating patterns in obese people, and that could create a vicious circle, putting them at risk for even more disordered eating," says Dr. Small.
No he didn't, he said... something in Greek. Why does the Wall St Journal feel the need to use a translation into faux-archaic English?