Here are four issues which have something in common - something which is overlooked by much of the left:

- Can we introduce a living wage without pricing some workers out of jobs?

- Can we tax companies more heavily without them moving their profits overseas, or cutting investment or shifting the burden onto workers or customers?

- Are there some macroeconomic policies - fiscal policies, wage-led growth, NGDP targeting (pdf) or whatever - that can create near-full employment?

- Is it possible to regulate banks sufficiently to avoid another financial crisis, whilst ensuring that they lend sufficiently to productive businesses?

These look like separate issues. But in one sense they are not. They are all different facets of the same question: how far can governments influence corporate decisions when they do not have direct ownership or control?

My answer, as regular readers know, is: not far. But that's not my point today. My point is rather that the non-Marxist left doesn't ask this question, but merely begs it.

In this context, the legacy of Keynes is a malign one. Although Keynes spoke of a "comprehensive socialization of investment", he swiftly mitigated this:

It is not the ownership of the instruments of production which it is important for the State to assume. If the State is able to determine the aggregate amount of resources devoted to augmenting the instruments and the basic rate of reward to those who own them, it will have accomplished all that is necessary.

And here;'s the problem. The "if" in that second sentence is a big one. For decades, however, the social democratic left has assumed that it's not, and that objectives of rough equality and full employment can be achieved within the constraints of capitalist ownership.

In fairness, this was more or less the case in the post-war years (although much of the "commanding heights" of the economy were nationalized then). But this broke down in the 1970s - a fact with which social democrats have never truly got to grips with.

And perhaps they won't - until they start posing the question they have ignored, of whether, perhaps, capitalist ownership is more of an obstacle than they have assumed. I don't know what the answer is here - though I have my suspicions! But if Labour is to be a serious policy-making party, rather than a mere marketing operation, shouldn't it at least ask the question?