The paper argues that Harrodian instability is an instance of what Hicks in his book Capital and Growth (1965) called static instability, related to the direction (and not to the intensity) of the disequilibrium adjustment process. We show why such instability obtains in demand‐led growth models in which the ratio of capacity creating private investment to output ratio is given exogenously by the aggregate marginal propensity to save. We also show that Sraffian Supermultiplier model overcomes the Harrodian instability and that its demand‐led equilibrium is statically stable. It is explained that the latter results do not follow from the presence of autonomous non‐capacity creating expenditure component as such but from its presence within a model in which investment is driven by the capital stock adjustment principle (i.e., the flexible accelerator). Finally, we argue that, although being statically stable, the equilibrium growth path of the Sraffian Supermultiplier model can be dynamically stable or unstable depending on the intensity of the reaction of investment to demand. We then provide a discrete time sufficient condition for the dynamic stability of such equilibrium that implies that the marginal propensity to invest remains lower than the marginal propensity to save during the adjustment process, a modified Keynesian stability condition.

Thirlwall's law, given by the ratio of the rate of growth of exports to the income elasticity of imports is a key result of balance-of-payments-constrained long-run growth models with balanced trade. Some authors have extended the analysis to incorporate long-run net capital flows. We provide a critical evaluation of these efforts and propose an alternative approach to deal with long-run external debt sustainability, based on two key features. First, we treat the external debt-to-exports ratio as the relevant indicator for the analysis of external debt sustainability. Second, we include an external credit constraint in the form of a maximum acceptable level of this ratio. The main results that emerge are that sustainable long-run capital flows can positively affect the long-run level of output, but not the rate of growth compatible with the balance-of-payments constraint, as exports must ultimately tend to grow at the same rate as imports. Therefore, Thirlwall's law still holds.

Resumo Estudos recentes indicam que a elasticidade-preço das importações brasileiras é baixa. Este trabalho procura racionalizar o referido resultado revisitando as estimativas das importações do país desagregadas por “categoria de uso”. Os resultados reportados sugerem que a baixa elasticidade-preço das importações agregadas reflete fundamentalmente a baixa elasticidade-preço das importações de combustíveis, bens intermediários e de alguns tipos de serviços - notadamente, transporte, aluguel de equipamentos e pagamentos de royalties - produtos que, somados, respondem por pouco menos de dois terços do total importado. Isso ocorre porque vários desses produtos têm pouca ou nenhuma possibilidade de substituição por similares nacionais, devido principalmente a deficiências estruturais na oferta nacional.

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