The law hasn't decided, because it has 17 words in the Human Rights Act which say we have to respect something it doesn't actually define.
And we haven't decided, because one minute we're desperate to know which footballer's taken out a super-injunction and the next we're outraged someone took a photo of the future queen's jubblies, while doing a Google image search to see them for ourselves.
People claim privacy when what they really want is secrecy, and there are plenty who trade it in return for cash, attention or glory.
It's a hazy concept with, on the one hand, obviously private individuals like the families of Milly Dowler and Madeleine McCann thrust into the spotlight by events and staying there in an effort to find their daughters, and on the other self-publicising meaningless starlets like Sienna Miller.
Sienna has had her share of unwelcome and unreasonable attention. She accepted £100,000 damages from the News of the World after it admitted hacking her phone, and gave evidence to the Leveson Inquiry about being hunted by marauding packs of paparazzi.
She said: "I would often find myself almost daily, I was 21, at midnight running down down a dark street on my own with 10 big men chasing me. The fact that they had cameras in their hands meant that that was legal. But if you take away the cameras, what have you got? You've got a pack of men chasing a woman, and obviously that's a very intimidating situation to be in."
Quite right she was too, sounds awful. In my experience though photographers generally just want a photograph, and if you give them one rather than legging it around alleyways life is a lot simpler. But if you're only 21 you're not to know that, necessarily.
Except that at the age of 21 Sienna was barely known, and a model rather than an actress. Her acting debut in a forgettable film was a year earlier in 2001, followed by another dud movie and a couple of unwatched TV series. After modelling for Coca Cola and Vogue, a breakthrough came in 2003 when aged 22 she posed in a thong, legs akimbo, for the Pirelli calendar.
Shortly afterwards she was cast in Layer Cake and then as Jude Law's love interest in the remake of Alfie, and when the film came out in 2004 it transpired they were a couple. Cue lots of interest in the photogenic, unknown actress girlfriend of the British acting megastar.
That year she went with the megastar to the Oscars, wearing a dress by up-and-coming designer Matthew Williamson for whom, by that point, she was 'a muse'.
During the following year or so both were undeniably hacked by the News of the World's private investigator, followed, and had every cough and spit of their lives spread over the newspapers. Sienna was 23 by this point, and that must have been difficult and uncomfortable.
Particularly when, in 2005, Jude made a public apology after being caught cheating on her with his children's nanny. It transpired Sienna had a fling with Layer Cake co-star Daniel Craig, one of Jude's mates. Then Jude and his ex Sadie Frost were found to have been wife-swapping with the drummer from Supergrass.
All pretty tawdry, none of it Sienna's 'fault' as such, and it was in this period she was followed most by the paps. She was 24, which is still young, but not as young as 21.
And to some extent attention is perhaps to be expected if you get engaged to a very famous person, split up, get back together again, generally take your clothes off in films, appear in public in nipple-baring frocks and give interviews in which you discuss your love life to promote your latest project.
That doesn't make being chased by 10 men down alleyways all right, of course. But being regularly chased down alleyways might make a person check their nipples are covered when in public, now and again.
She got a few more film roles, nothing startling, which in 2008 included appearing in a film called Hippie Hippie Shake which nobody noticed except for the fact Sienna was employed to take her clothes off in it.
During one bit of filming, in the middle of a London park, Sienna was starkers in a pond filming a scene when an enterprising snapper snuck a few shots of her.
Now it's not nice being photographed when you don't know about it, but it was in a public place and there was a whole film crew on hand. Sienna was aware people would be looking, and that ultimately her boobs and bits would be projected on screens 30ft high for the public to gawp at.
Another picture, in that situation, is neither here nor there and what's more became the only useful bit of publicity the film got.
Sienna felt differently, and sued the newspapers which published the picture and won £37,500 for her trouble, which incidentally is more than the film ever made at the box office because it was never released. The production company was losing cash and canned the whole thing.
Around the same time she launched into an affair with the billionaire married father-of-four Balthazar Getty. They were pictured in public on a yacht in Italy, while Sienna was topless and cuddling a man she shouldn't have been.
Sienna sued the newspapers which printed the pictures, gave interviews saying she had ended the fling, that she was still in love with Jude Law, was asked by Jude to please stop talking about him, and then was seen again canoodling with Getty.
More recently, Sienna has settled with a new boyfriend and had a baby who she has been more than happy to gossip about with journalists to promote her latest film project.
And, today, it's been revealed she has posed in all her naked eight-months pregnant glory for an oil painting.
So - and let's be clear here, and use logic - Sienna's idea of privacy is what, exactly?
Because it looks to me as though she is entirely happy to trade on her baby, her boobs, and her lovers when it's on her terms and takes great offence if anybody inquires about any of them when it doesn't benefit her in some way.
It looks like she is happy to mislead a public inquiry into the ethics of the media while, thankfully, not having her own ethics questioned in the least.
It looks like the acting has not been as successful as the suing was, and it especially looks like when the harassment she complained of stops she responds by getting her kit off in such a fashion as to draw more attention back to herself.
It's a million miles from the intrusion suffered by the Dowlers and McCanns, and hardly in the same field as Kate Middleton being snapped topless a good mile from a public road.
Sienna once boasted she had changed the law on paparazzi and that "they can't take photographs of me anywhere I expect privacy. They can't sit outside the house, follow in cars – unless I'm coming out of The Ivy, which I'm not going to be".
Except that it was already the case that photographs cannot be taken anywhere people expect privacy, and it's entirely legal to sit outside someone's house unless they feel harassed in which case there's a law for that already too.
No, all Sienna has done is prove, with a quite majestic degree of hypocrisy, how much of a two-faced little baggage she is and how stupid judges and lawyers can be when faced with a pretty blonde whose tits they can all picture.
She doesn't get intruded upon anymore, which for some reason makes her all the more keen to thrust her publicity-hungry breasts at us whether we like it or not while barking about how awful it makes her feel.
You know, I never thought she was much of an actress.