"Honey, I bought us a robotic vacuum cleaner! Now you can send the maid back to Manila!"

Mechanization and automation have produced great results in manufacturing industry. Productivity -- roughly, output per hour of an employee's time -- has increased remarkably; similarly, wages have increased, possibly rather less so. It is undoubtedly true that the average factory job in the top industrialized countries is much more rewarding, in several senses, now than 100 years ago.

One could debate whether this would still be the case if it weren't for the contribution that the many millions of people still working in sweatshop conditions for derisory wages make to "keeping costs down" globally. But a different fact that leads us to question whether automation is a panacea against repetitive, degrading drudgery is the decline in manufacturing employment in the industrialised countries and the rise of the service sector.

It's true that lots of people were put out of work by the machines, but it's also true that lots of them got jobs elsewhere. What kind of jobs? So far, even the most "advanced" societies appear to require menial tasks of their members: trash-can emptying, burger-flipping, dishwasher-loading, toilet-cleaning, data entry, tech support... The question is, when capitalism finally triumphs and everyone in society is rich, who will be picking up litter from the streets? Robots are the only honest answer. But, given current rates of R & D, the development of such automated servants is likely decades away. Would you trust a self-cleaning toilet, or tolerate an automated telephone response when you phoned to tell the company that your lawnmowing robot was on the fritz and had decimated your lobelias? Nevertheless, let's conduct a little economic thought experiment.

Suppose that, due to an amazing technological spin-off from the space programme, all the menial service jobs were, from tomorrow, done more cheaply by robots. Then all the people doing them would be out of work, or have to take pay cuts. Conversely, robot manufacturers would have to take on lots of additional staff. But, the number of additional robot factory staff would be much less than the number put out of work, since to do the same menial jobs the robots are cheaper, and the cost of buying and running a robot includes at least the robot factory wages, overheads and raw materials, and we assume that the robot factory workers are better-paid than the erstwhile bottlewashers.

Then you argue that the money saved by using robots is now going on other, non-menial, services, like attending concerts or building architect-designed houses. Fine, except that you have to turn people who spent the last decade emptying trash cans into highly-skilled professionals, and the same amount of money employs a hell of a lot fewer architects than it does call centre drones. So you need extensive, and intensive, training programs and steady, vigorous economic growth - otherwise the effect of cheap robots would be to drive low-wage jobs even lower and hand the bonus to the professional class. In short, you need sustained full employment, which creates the incentive for employers to train recruits to the level where their skilled labour is both profitable and rewarding.

Conversely, if we were in a situation where the wages for unskilled labour were rising well above inflation, there'd soon be big opportunities in automating menial jobs. Such a condition has occurred exceedingly rarely in the last century or so, and always accompanied by inflation that in the medium term crippled the growth that gave rise to it. Or else, some of those millions of people overseas doing harder work for less money come on over to put the kybosh on any prospect of robotic Utopia.

The depressing fact is that most people in the world would experience a several-hundred-percent pay increase by taking menial work in the U. S., and do a better job into the bargain; it's only protectionism and lack of mobility that stops them doing so. If the age of robotic servants comes as a result of true global prosperity, my distant descendants will truly have found heaven on Earth. Automation of service jobs in my lifetime can only come as a result of closed-border policies that exacerbate global inequality.