Class is about scale. The clue’s in the name. Class is a collective noun, one that is used to help us observe deep social forces in motion. And to see these forces in motion, you need to step back and look at the bigger picture.
The main way that this is done is through occupations, as the dispersion of occupations throughout the economy gives us a good indication of the type of goods and services at play in the economy, and the type of economic forces which drive it. But, what is being observed is occupation, not people.
Now, for many people their job is a large part of their lives, and the income they get from that job has quite an influence on their purchasing power, which happens to be the dominant power in a capitalist economy. Denis O’Brien has a lot more purchasing power, for example, than the Haitians who work for his mobile network. Different occupations have different levels of decision-making autonomy, so that within the workplace there are power relations at play as well.
What is being observed is the dynamics of macro forces. Denis O’Brien is an individual. He is also a venture capitalist. And within a capitalist economy, venture capitalists have a lot more purchasing power than cleaners, or IT workers.
I suppose what I’m saying is that if you really want to know whether something is an arse or an elbow, you need to step back and look at the bigger picture, because it’s only the scale provided by the bigger picture that can answer that question.