A pergunta continua a não ser consensual na doutrina económica, especial, naquelas (quase todas) que defendem que a decisão seja por decreto, mas sempre dirá que ajusta a taxa de juro à inflação (ou expectativa... ou whatever) e ao crescimento e produtividade do capital. Os Keynesianos dirão que é o prémio para se afastar de liquidez, o que é um bocado estranho no sentido em que qualquer preço então (o de uma cerveja por exemplo) representa um prémio para se afastar de liquidez -> moeda). Os austríacos dizem que o juro representa simplesmente uma preferência subjectiva temporal (não está sujeito a óptimos ou optimizações sociais) entre o consumo presente e bens futuros.
The Austrians on Interest
When it comes to explaining the coordinating function of market prices, Austrians assign a very important role to interest rates, for they steer the deployment of resources over time. Loosely speaking, a high interest rate means that consumers are relatively impatient, and penalize entrepreneurs heavily when they tie up resources in long-term projects. In contrast, a low interest rate is the market’s green light to entrepreneurs that consumers are willing to wait longer for the finished product, and so it is acceptable to tie up resources in projects that will produce valuable goods and services at a much later date.
In the Austrian conception, it is the interest rate that allows the financial decisions of households to interact with the physical capital structure, so that producers transform resources in the ways that best satisfy consumer preferences. Consider a simple example that I use for undergraduates: Suppose the economy is in an initial equilibrium where households save 5 percent of their income. Then the households decide that they want to have more for their retirement years, because they don’t want their standard of living to plummet once they stop working. So all the households in the community begin saving 10 percent of their income.
In the Austrian view, the interest rate is the primary mechanism through which the economy adjusts to the change in preferences. (It’s not that people switched from buying hot dogs to hamburgers; instead they switched from buying “present consumption” to buying “future consumption.”) The increased household saving pushes down interest rates, and at the lower rates businesses can start long-term projects. From the individual entrepreneur’s point of view, the interest rate affects the profitability of longer projects more than shorter ones (as a simple “present-discounted-value” calculation shows). So a lower interest rate doesn’t merely stimulate “investment” but actually gives a greater inducement to investment in durable, long-term goods, as opposed to investment in nondurable, short-term goods.
How is it possible that the community as a whole can have more income in, say, 30 years? Obviously the households think it is financially possible, because their bank balances rise exponentially with the higher savings rate. But technologically speaking, this is possible because the composition of physical output changes. The households have cut back on going out to dinner, buying iPods, and so on, in order to double their savings rate. This means that restaurants, Apple stores, and other businesses catering to consumption will have to lay off workers and scale back their operations. But that means labor and other resources are freed up to expand output in the sectors making drill presses, tractors, and new factories.
In 30 years, the economy will be physically capable of much higher output (including the production of consumer goods), because at that time, workers will be using a larger accumulation of capital or investment goods made during the previous three decades. That is how everybody can have a higher standard of living, through savings.