There is a presumption that it will not be sustainable if inflation soars or if the balance of payments gets too far out of line. Thus, it is sometimes postulated that the objective of macroeconomic policy should be to maximize growth subject to two constraints: that inflation remains within limit of tolerance and the current account deficit in the balance of payment remains within manageable proportions. And, often, it is very difficult to anticipate which of these problems will arise or which of the constraints will become binding. Maximizing growth typically means maximizing current output and employment, if labour productivity growth is constant or exogenous.