In Theories of Surplus Value, Marx writes:
Assume that the productivity of industry is so advanced that whereas earlier two-thirds of the population were directly engaged in material production, now it is only one-third. Previously 2/3 produced means of subsistence for 3/3; now 1/3 produce for 3/3. Previously 1/3 was net revenue (as distinct from the revenue of the labourers), now 2/3. Leaving [class] contradictions out of account, the nation would now use 1/3 of its time for direct production, where previously it needed 2/3. Equally distributed, all would have 2/3 more time for unproductive labour and leisure. But in capitalist production everything seems and in fact is contradictory… Those two-thirds of the population consist partly of the owners of profit and rent, partly of unproductive labourers (who also, owing to competition, are badly paid). The latter help the former to consume the revenue and give them in return an equivalent in services—or impose their services on them, like the political unproductive labourers. It can be supposed that—with the exception of the horde of flunkeys, the soldiers, sailors, police, lower officials and so on, mistresses, grooms, clowns and jugglers—these unproductive labourers will on the whole have a higher level of culture than the unproductive workers had previously, and in particular that ill-paid artists, musicians, lawyers, physicians, scholars, schoolmasters, inventors, etc., will also have increased in number.A large and growing share of employment, in other words, is unnecessary from a technical standpoint. It exists because useless jobs are more conducive to social stability than either mass poverty or a social wage. The payments the majority of the population receives for not rioting or rebelling look better when they are dressed up as payment for our work as mistresses, grooms, jugglers -- or as yoga instructors or economics professors. This way, people are still dependent on a boss. In a differently organized world, we could dispense with most of these jobs and take the benefits of increased productivity in some combination of shorter hours for productive workers and a shift toward more intrinsically fulfilling (craft-like) forms of productive work.
By starting from here we can think more sensibly about employment and unemployment. From a macroeconomic standpoint, all we need is that expenditure on unproductive labor changes in some rough proportion with income.
From my point of view, the essential facts about employment are (1) As long as the most socially accepted form of claim on the social product is wages for work, work will be found for people, along the lines Marx suggests. (This is not true in poor societies, where a large portion of the poor engage in subsistence labor, of either the traditional or garbage-picking variety.) And (2) In the short run, employment will rise and fall as the rich feel a smaller or a greater need for the insurance-value of financial wealth.
As soon as you being to think about employment in terms of an input of labor to a production process, you've taken a wrong turn. We should not try to give supply-based explanations of unemployment, i.e. to show how the allocation of some stock of productive resources by some decision makers could generate unemployment. Unemployment is strictly a phenomenon of aggregate demand.
Unemployment in advanced countries is not characterized by exogenous factor supplies and Leontief-type production functions, where some factors are exhausted leaving an excess supply of their complements. (The implicit model that lies behind various robots-will-take-all-the-jobs stories.) Unemployment in capitalist economies involves laid-off workers and idle factories; it involves unemployed construction workers and rising homelessness; it involves idle farmworkers and apples rotting on the trees. Unemployment never develops because we need fewer people to make the stuff, but because less stuff is being made. (Again, things are different in poor countries, and in the early stages of industrialization historically.) Unemployment cannot be explained without talking about aggregate demand any more than financial crises can be explained without talking about money and credit. It exists only to the extent that income and expenditure are determined simultaneously.
Unemployment rises when planned money expenditure falls for a given expected money income. Unemployment falls when planned money expenditure rises for a given expected money income. Conditions of production have no (direct) effect one way or the other.
Recognizing that unemployment is an aggregate expenditure phenomenon, not a labor-market phenomenon, helps avoid many errors. For example:
It is natural to think of unemployed people as people not engaged in productive work. This is wrong. The two things have nothing to do with each other. Unemployed people are those whose usual or primary claim on the social product takes the form of a wage, but who are not currently receiving a wage. There are lots of people who do not receive wages but are not unemployed because they have other claims on the social product — children, retirees, students, caregivers, the institutionalized, etc. Almost all of tehse people are capable of productive work, and many are actively engaged in it — caregiving and other forms of household production are essential to society’s continued existence. At the same time, there many people who do receive wages but who are not engaged in productive work; one way to define these is as people whose employment forms part of consumption out of profits or rents.
While there is no relationship between people’s capability for and/or engagement in useful work, on the one hand, and employment, on the other, there is a close link between aggregate expenditure and employment, simply because a very large fraction of expenditure takes the form directly or indirectly of wages, and aggregate wages adjust mainly on the extensive rather than the intensive margin. So when we see people unemployed, we should never ask, why does the production of society’s desired outputs no longer require their labor input? That is a nonsense question that will lead nowhere but confusion. Instead we should ask, why has there been a fall in planned expenditure?
Going beyond the 2012 conversation, two further thoughts:
1. The tendency to talk about unemployment in terms of why some peoples' labor is no longer needed for production, is symptomatic of a larger confusion. This is the confusion of imagining money claims and payments as a more or less transparent representation of physical and social realities, as opposed to a distinct system that rests on but is substantially independent from underlying social and biological existence. Baseball requires human beings who can throw, hit and run; but the rules of baseball are not simply shorthand for people's general activity of throwing, hitting and running. Needless to say, economics education assiduously cultivates the mixing-up of the money game with the substrate upon which it is played.
2. It's natural to think of productive and unproductive labor as two distinct kinds of employment, or at least as opposite poles on a well-defined continuum. Marx usually writes this way. But I don't think this is right, or at least it becomes less valid as the division of labor becomes more extensive and as productive activity becomes more directly social and involves more coordination of activities widely separated in space and time, and more dependent on the accumulation of scientific and technical knowledge.
Today our collective productive and creative activity requires the compliance of a very large number of people, both active and passive. This post will never be read by anyone if I don't keep on typing. It will also never be read if the various tasks aren't performed that are required to operate the servers where this blog is hosted, my internet connection and yours, the various nodes between our computers, the utilities that supply electricity to all the above, and so on. It would not be read if someone hadn't assembled the computers, and transported and sold them to us; and if someone hadn't developed the required technologies, step by step as far back as you want to go. It would not be read, or at least not by anyone except me and a few friends, if various people hadn't linked to this blog over the years, and shared it on social media; and more broadly, if the development of blogs hadn't gotten people into the habit of reading posts like this. Also, the post won't be read if someone breaks into my house before before I finish writing it, and steals my laptop or smashes it with a hammer.
All of these steps are necessary to the production of a blog post. Some of them we recognize as "labor" entitled to wages, like whoever is watching the dials at Ravenswood. Some we definitely don't, like the all-important not-stealing and not-smashing steps. And the status of some, like linking and sharing, is being renegotiated. Again, a factory only runs if the workers choose to show up rather than stay home in bed; we reserve a share of the factory's output to reward them for making that choice. It also only runs if passersby choose not to throw bricks through the windows; we don't reserve any share of the output for them. But if we were going to write down the physical requirements for production to take place, the two choices would enter equivalently.
In a context where a large part of the conditions of production appear as tangible goods with physically rival uses; where the knowledge required for production was not itself produced for the market; where patterns of consumption are stable; where the division of labor is limited; where most cooperation takes the form of arms-length exchanges of goods rather than active coordination of productive activity; where production does not involve large commitments of fixed capital that are vulnerable to disruption; then the idea that there are distinct identifiable factors of production might not be too big a distortion of reality. In that context, splitting claims on the social product into shares attributable to each "factor" is not too disruptive; if anything, it can be a great catalyst for the development of productive capacities. But as the development of capitalism transforms and extends the division of labor, it becomes more and more difficult to separate out which activities that are contributing to a particular production process. So terms like productivity or productive labor lose touch with social reality.
You can find this argument in chapters 13-14 and 32 of Capital Volume 1. The brief discussion in chapter 32 is especially interesting, since Marx makes it clear that it is precisely this process that will bring capitalism to an end -- not a fall in the rate of profit, which is never mentioned, nor a violent overthrow, which is explicitly rejected. But that thought will have to wait for another time.