What public spending can be financed by public debt?

It would be extremely useful to know precisely which public spending and which public investments have a significant positive effect on productivity gains and therefore on long-term growth. This would make it possible to know which public investments and which public spending can be financed by public debt, since the additional growth will generate additional tax revenues that will make it possible to repay the debt. This would also make it possible to intelligently reform the European fiscal rules. When we look across OECD countries to see which government spending appears to have a positive effect on productivity, we find that this is the case: For education, healthcare, research and development; But not for pensions, defence, justice and security, family, housing, the labour market, public investment and economic action. This shows how difficult it is to draw up a list of “productive” public spending: We cannot debt finance all education, healthcare and R&D spending; we must therefore look at a much finer level than this general level to see which public spending increases productivity; Public debt financing cannot be authorised for public investment, which is often proposed, since public investment does not seem, taken as a whole, to have a positive effect on long-term growth; Some types of public spending are important for the population's well-being (justice, security, defence, family, housing, labour market), but do not have a positive effect on growth: they must therefore be tax financed.