Previous columns in this series looked at the major classes in society. They considered the two major groups in advanced capitalism - the working class and the capitalist class. Between them stands the 'traditional middle class' - layers of shopkeepers, small businessmen (such as pub landlords), and some professionals who run their own practices, such as most GPs, dentists and high street lawyers.
These are essentially the same groups Karl Marx and 19th century socialists referred to when they used the term petit bourgeois, meaning 'little capitalists'. But there are other layers in modern capitalism sandwiched between the working class majority and the tiny capitalist ruling class. There are all sorts of categories of managers in both the private and public sectors.
They don't run 'little capitalist' enterprises as shopkeepers do. Instead they are part of a bureaucracy and are salaried employees - drawing a wage either from the government or those at the top of the company. The traditional middle class has shrunk over the last century. The 'new middle class' has grown. The reason for this is the development of capitalism.
Large companies have gobbled up smaller ones to create major corporations. So in banking, for example, half a dozen companies dominate the market - whereas in the mid-19th century there would be a host of local banks. Such changes have turned bank clerks from virtual partners in a small firm into white collar workers employed by giant companies.
A traditional middle class profession has been 'proletarianised' - most of its members have become workers. The other side of this process has been the creation of bureaucratic hierarchies to run the giant companies. In corporations today there is a vast space between the handful of major shareholders and directors, and the mass of workers.
The space is filled by a pyramid of managers who take on the functions that capitalists themselves used to do-organising production and, crucially, disciplining the workforce. It is hard to pin down exactly where this layer begins and ends. At the top it shades into the ruling capitalist class - getting big share options just as top bosses do, and therefore identifying with the multimillionaires.
At the bottom it starts to blend with the mass of the workforce. Lower level line managers get higher wages than the workers, but not several times more. They are subject to harsh discipline from above in order to make them discipline those below.
That is also the picture in the public sector bureaucracies. They grew enormously after the Second World War as the state took on the role of providing things the capitalists as a whole needed - an educated workforce, a transport system and so on. In any hospital there are all sorts of people (often linked to business) between trust bosses and nurses, porters and other health workers.
Headteachers are encouraged to see themselves as managers. In a large secondary school there will be a head, half a dozen members of senior management, and over 100 teachers and support staff. This new middle class is pulled in two directions - to identify with the capitalists and top state bureaucrats above them, or to share some of the feelings of the workers.
Line managers can be vicious disciplinarians but may also moan to workers about top bosses or voice the same fears about redundancy.
The picture is further complicated by the way policies such as privatisation have created divisions inside the new middle class.
A small number of headteachers, for example, have been offered huge pay rises to become 'super-heads', embracing free market initiatives or overseeing a number of schools. Many headteachers, however, see themselves as part of a public education system, although a well paid part of it. So there is currently a revolt by the majority of headteachers, who do not want to implement the government's divisive payment by results scheme. Opposition to a part of the capitalist system from those who are a cog in the machine is important, especially when there is a deep social crisis.
Sections of the middle class, new and old, took to the streets of Argentina. That inspired a wider process drawing in more powerful social forces, above all the working class. But the new middle class remains caught between the two major classes, capitalists and workers.
The same middle class groups that protest against a government can rush to defend it if they fear a far wider revolt by workers. That means workers organising to fight themselves, even when they are on the same side as those just above them over an issue.