It is probably better to contrast capitalism with socialism though, and classical economics with communist theory. Not all capitalists ascribe to classical economics, just like not all socialists ascribe to communist theory.
Marx gave capitalism a name to talk about it as a step in the thrust of history, contrasting it with earlier feudalism systems, and to argue that it would inevitably lead to its own destruction while advocating that communism is the logical next step. It wasn't just "anything before communism" even for him.
Keynes, Hayek, and Smith all have a common thread on their belief in the market, despite the fact that they would in many cases advocate for very different policies.
Is anything about that theory specific to any time period? Does any part of it refer to a system of "capitalism"?
Marx, and those following Marx, wrote their works under the banner of "communism". Adam Smith did not write under any banner. He made observations.
> Marx gave capitalism a name to talk about it as a step in the thrust of history, contrasting it with earlier feudalism systems, and to argue that it would inevitably lead to its own destruction while advocating that communism is the logical next step. It wasn't just "anything before communism" even for him.
You're not getting what I'm saying. Marx gave capitalism a name, OK. Did he give it a definition? The whole problem I'm talking about here is that people use the word "capitalism" without having a meaning in mind for it to refer to.
> The history of capitalism is diverse. The concept of capitalism has many debated roots, but fully[quantify] fledged capitalism is generally thought by scholars[specify][weasel words] to have emerged in Northwestern Europe, especially in Great Britain and the Netherlands, in the 16th to 17th centuries.[citation needed] Over the following centuries, capital accumulated by a variety of methods, at a variety of scales, and became associated[by whom?] with much variation in the concentration of wealth and economic power. Capitalism gradually became the dominant economic system throughout the world.[1][2](subscription required)[need quotation to verify][3][need quotation to verify] Much[quantify] of the history of the past 500 years is concerned with the development of capitalism in its various forms.
> It is an ongoing debate within the fields of economics and sociology as to what the past, current and future stages of capitalism are.
This does not leave me filled with confidence that people know what they mean when they mention "capitalism".
The problem is that there are two broad paradigms of what "capitalism" should mean:
1. Whatever the United States does.
This is what most people seem to be talking about when they talk about "capitalism", but it leaves something to be desired on theoretical grounds. Many aspects of it are not particularly economic.
2. An economic system defined... somehow. Mostly by constrast with "communism", which -- unlike "capitalism" -- has a large body of theory attached.
This is what people want to claim they are talking about. It is more or less conceptually incoherent, being defined only as the absence of policies covered by the term "communism". But all of those negative policies are very old, historically.