Yeah, I know, Marx wrote three volumes on this, and in 2014 Piketty published in English a more than 700 page book on it that ended up on the bestseller list, although neither of these resolved the long-running debates about the nature of profit or of capital, which continue to swirl. We have seen recently someone claiming that distinguishing between retained and distributed earnings is the key to understanding profit, and failing to do so means all of economics as we know it is wrong. But then there have been many other views that this view does not remotely address. Regarding capital itself, which profit is usually thought of as being one of the sources of income related to, let me quote the following that notes a range of views out there.
“What really is capital and what does it mean for value, growth, and distribution? Is it a pile of produced means of production? Is it dated labor? Is it waiting? Is it roundaboutness? Is it an accumulated pile of finance? Is it a social relation? Is it an independent source of value? The answers to these questions are probably matters of belief.” From Catastrophe to Chaos: A General Theory of Economic Discontinuities, Kluwer, 1991, p. 125.
I leave it the imagination (or googling) of the reader as to who the author of that book is, although I note that the quotation appeared in the second edition of the book that came out in 2000.
So there are surface issues regarding the nature of profit and capital, and there are deeper issues. This quotation lists some of the deeper arguments that have been made by different schools of economics. The “pile of produced means of production” is basically a Principles textbook orthodox position, which rules out financial definitions, with many “people in the street ” thinking it is an “accumulated pile of finance,” a later answer in the list. People teaching intro econ courses like to pound on wrongness of this popular view, ultimately falling back on the argument that capital is a “factor of production,” which means that whatever it is one must be able to use it in actual production processes.” Machinery and buildings and other such “produced means of production” do that, so they count, and the building of them is what “real investment” is, not just somebody using some money to buy some financial assets, which is what the person in the street usually means by “investing my capital.” We spend lots of time disabusing them of their delusions, we who know that “money is an illusion,” and that while finance is very important in the functioning of modern economies, piles of money or financial assets do not in and of themselves actually produce something. Rather they are indicators and means for determining who gets to own those actually productive forms of “real capital,” oh to throw out another term.