[danans]

It's just a classification system, so I wouldn't take it in isolation. If what you are trying to understand is wealth and power, you have consider more dimensions.

In Marx's time, these categories perhaps mapped more consistently to the gradation of wealth and power, but there were exceptions then too.

And the degree to which an asset is "capital" that produces wealth and income without the owner's labor is relative to it's scarcity. The 30k car is a common possession, and also it has no added economic value without the driver's direct labor. A fleet of cars driven by rented labor is capital, as are factories, valuable land, or high concentrations of wealth.

Education is a kind of capital, but the surgeon's student loan is no different in than a social worker's student loan, except in the cost and income potential.

In that sense the surgeon is a worker but their work usually produces a great deal of extra income that allows them to purchase capital assets of other kinds.