Alternative models of balance-of-payments or exchange-rate determination

What causes changes in the sum of the autonomous items in the balance of payments, which in turn causes either payments disequilibria or alterations in exchange rates? Those factors that would cause a balance-of-payments deficit

for a country maintaining a fixed parity would instead cause a depreciation of the currency if a floating exchange rate existed. Accordingly, we are seeking to explain exchange market pressures that can result in changes either in the balance of payments or in the market exchange rate.