I never understood why "There, there" is supposed to cheer someone up. Does anyone know?
I don't think it's got much to do with the meaning of the word "there" at all.
It's just a soothing sound that's fairly easy to make. If you repeat it enough times I'm sure it has a somewhat hypnotic effect. Like humming baby to sleep.
LATER: One could go on forever postulating soothing words that could rationally follow one meaningful utterance of the word, but I think this is pointless. It's a kind of mantra, just not as meaningful as Om mani padme hum Which I didn't know meant anything either, until Wikipedia just informed me. But I still wouldn't believe Wikipedia if it told me why we say "There there".
I'll also just point out that earlier on we're much more likely to say "Here" to a distressed child, while presenting a sweet, comforting toy, cuddle, or whatever. Even to a baby too young to understand any words. But curiously, repeating that word rapidly turns it into either an admonition or something cheerleading British MPs say when one of their party scores a political point in 'Parliamentary debate' (if that's not an oxymoron).
In short, the meaning of "There there" is irrelevant to usage, as well as origin.
The OED links this usage to the use of there as an interjection to denote a sort of verbal finger pointing (e.g., There, I fixed it):
there, adv. (adj. and n.)
7 . Used interjectionally, usually to point (in a tone of vexation, dismay, derision, satisfaction, encouragement, etc.) to some fact, condition, or consummation, presented to the sight or mind. Hence there-there vb. trans., to soothe or comfort by saying these words.
I'm not sure I understand the connection, but there you have it.
I found a Word Detective article with some interesting suggestions:
The consolation of that "there's always next year" is the key to "There, there" as a comforting verbal gesture. Its role is to say "Look there, there's something good amid the bad." In fact the comforter often goes on to name the supposedly consoling thing, as in "There, there, she wasn't your type anyway" or "There, there, it's only money."
The article also deconstructs similar verbal mechanisms such as now, now.
I have no references for the following opinion.
We do use the fragment
to signify not only location, but also more importantly that it is a right location. This is an example when someone is looking for something and we are looking for it too (or helping someone find it).
"There" in this case signifies that you found the spot, that you are doing something right and delivers a positive message of support. In this case usually the intonation is excitement, urgency or exclamation.
The use of double signal
emphasize the positive message and is usually delivered in calm and supportive tone. As if you have already found what you need or what you are looking for. Here it confirms or reconfirms that things are ok.
This should be enough for possible etymology, but also note that the expression is also used with very small children who can not even understand the spoken language. Therefore, the sound and the intonation do most of the work here and I would say are equally important as any etymology, true or false.
Re: the possible origins of "there, there." Sorry this entry is based on impersonal experience. It seems eminently plausible that in prehistoric times cave persons would keep a wary eye out for marauding beasts. So, say if a monster (not to be pejorative) were spotted by an individual who helpfully pointed out the threat to others but they couldn't quite make it out - as presumably -eye glasses had yet to be invented - they would ask with some degree of concern "Where? Where?" The response - of course - would be "There! There!" Small comfort yet a bit reassuring. Maybe it's a survival thing then.