Piketty says something in a way that sounds like he takes it, as so many do, as axiomatic:

“…growth always includes a purely demographic component and a purely economic component, and only the latter allows for an improvement in the standard of living.”

The nit I’d like to pick with this received trusim is marginal relative to its broad accuracy, but is still worth noting – there are economies of scale to absolute population. These manifest in two interrelated ways – consumption and investment choices that are only “unlocked,” if it were, when total population crosses certain thresholds, and future per-capita-growth that results from past choices that were contingent upon absolute population.

I can illustrate these by giving three examples – one purely the former, one purely the latter, one a mix.

A purely “unlocked” choice would be a more specialized service that could not achieve scale relative to fixed costs without a large enough absolute population given a fixed share of population interested in the service. Think “shop that only sells customized meeples” or more conventionally “Latverian restaurant.” This doesn’t affect to the level of per-capita income or output, now or in the future, but improves living standards by providing a greater diversity of quality consumption options.

A purely future-oriented choice might be an aircraft carrier. Today, nobody benefits. But in the long term, if an aircraft carrier in the most optimistic framing maintains peace, security, and a stable order, this allows for greater per-capita growth (and fewer destabilizing interruptions) in the future, though in the present it registers as output that brings little utility to the public at large. Obviously two things must be noted –  military investment does not always increase peace, security, and stability; and even assuming it does, there are many, much more cynical, interpretations of how military power projection leads to future per-capita growth for the projectors.

A mixed choice would be cet bruyant objet du désir, a large subway system. It both increases consumption options and quality available to present individuals – lots of people prefer riding trains! – while also being an investment that increases long-term per-capita-growth rates.

This is not the most important point in the world, but since Piketty made it I found it a good time to quibble with it.