I mean, you always know what day of the week it is, or at least roughly which bit of the week you're in. Even if you wake up face down in a field wearing a clown costume you can tell this must be the weekend, or a Monday morning because Monday mornings are always bad.
But if in the future someone invented time travel and misprogrammed the flux capacitor so that they found themselves in Reigate right now, they wouldn't know what year it was.
They could wander around and work out from the temperature it was winter, and from the clothes it was some point after petticoats went out of fashion, but if they picked up a newspaper (completely ignoring the date printed on the front) and had a little read they wouldn't know when they were.
On the one hand it seems to be the 1970s, with football hooligans wreaking havoc, tossing coins at mixed race football players, being racist and generally making the beautiful game the kind of war zone we all thought was long past.
Elsewhere it looks like some time before Magna Carta, because a man convicted of rape who served his sentence and should have been released in 2002 has, instead, been in jail ever since. Stuff Habeas Corpus, we now lock up people for the crime of being from a country we think we're too nice to send them back to.
Then we've got children playing the age-old game of 'you show me yours and I'll show you mine' apparently infected by something not unlike the plague of 1348 with an epidemic of sexting sweeping the nations' schools and perverting everyone under the age of 12.
On top of all that the ruling class are lining their own pockets and writing their own rules about how that is allowed while at the same time demanding everyone else be open, transparent, genuinely accountable and independently regulated.
The government are trying to bring in a spy network that would have made Elizabeth I raise her eyebrows while outlawing the poor in a way she'd have been quite impressed by. Gropey men who may have earned slap from a grown woman in 1982 are being investigated by police probing a paedophile scandal no-one, but no-one, has yet been able to explain.
A Muslim man who's not been convicted of anything has been forced to leave his home, new census data is going to be used to herald the end of Britain as we know it and there seems to be serious discussion about whether gays are human beings.
I get confused about what year we're in all the time, so heaven knows what a misdirected time traveller would think. I suppose if you take an average it's probably somewhere in the 17th century, although whether it's before we revolted or after we decided to cancel all the fun I couldn't hazard a guess.
But then if we're feeling the effects of Puritanism before we've had the Civil War that would mean we're going backwards through time, which would at least explain Ashley Cole.
Unfortunately Einstein's not here to explain how that would work, and as we've long reversed past the time of his birth he's not about to reappear and help us figure it out. In fact science-wise we're probably about to start relying on plants.
So what do we do? Give up, and drift about on the sands of time as history endlessly repeats itself, pundits reheat the outrage they first served up a decade ago, and people wail and wheel from one disaster to another like peasants unable to scratch their own name in the dirt?
It's a radical thought but we could always tell ourselves it's the 21st century, and wise the hell up.
We could decide that if our children need mobile phones it's up to their parents to turn off picture messaging on the account which they're in charge of. Sexting's only an epidemic if children are paying their own bills; until then, it's just parents being inept.
We could wonder why children talk about sex earlier than they used to, and perhaps the answer would be because the adults all talk about it more as well. If you want the offspring not to look at porn, ask for or send pictures or treat each other as objects then it might be an idea to see how much of that seems to be normal to adults, and whether it is quietly noted by smaller people.
We could start acting like football is a fairly simple game, that it's not for racist, stupid, drunken, coin-throwing, pitch-invading, swearing and abusive idiots and that it would, frankly, be better without a lot of the footballers, too.
We could prosecute MPs whose actions seem to most people to constitute fraud, only lock up criminals proved beyond all reasonable doubt to deserve it, chillax about skin colour and realise that the definition of marriage has changed significantly over the years along with procreation. By law churches have to marry anyone who asks, with the right to opt out in cases such as divorced couples, and gay marriage would be no different. If they want to marry and the vicar wants to do it no-one from the 21st century gives much of a toss.
But then all that would involve acting like grown-ups, travelling in a forward motion, evolving as a result of our mistakes and getting wiser every day.
The fact we've been doing that quite successfully for millions of years appears to be no reason to continue, even though as a direct result we have fountain pens and Hob Nobs and drugs that stop cancer.
There may be some things about the modern world you don't like, humanity, but the trouble with going backwards is that eventually you reverse into the swamp on your hands and knees.
Rather you than me.