Much of contemporary economics does not view capital as dated labour inputs – a view popular with the Austrian School of Mises and Hayek, with clear antecedents in Marx (Karl, not Groucho). Instead it has just two kinds of inputs – instantaneously variable inputs, like labour and raw materials, and fixed inputs like capital goods. Instantaneously variable inputs are hired and immediately produce output which is sold on the market without any lags. Fixed input decisions are taken one year, the capital equipment is installed the next year and starts producing output for which is available for sale the year after that.
This view of the production process means that the cost of capital, interest rates and credit conditions, including credit rationing, don’t have any impact on potential output (supply) over horizons relevant for cyclical stabilisation policy. Their effect on demand, through fixed investment, inventory investment, consumption and net exports, is recognised of course, so the impact of tighter credit conditions, including credit rationing because of a credit crunch, is always assumed to be a lower output gap – demand falls but supply remains unchanged or, equivalently, actual output declines but potential output is unaffected in the short and medium term.
Once we recognise that all production takes time, credit conditions can influence effective supply (effective potential output) even in the short run. Labour is hired this month, produces output next month which is sold at the end of the month after that. Assuming labour is paid no later than the end of the month in which it is performed, the employer has to find enough credit to pay for one month’s worth of wages and one month worth of inventory of finished goods if he is to produce at all, even if the fixed capital is installed and ready to go.