Stocks hit a four-year high on Tuesday as equity markets continue to grind steadily higher on hopes that central banks will act in the near future to stimulate their economies.

The S&P 500 has risen more than 3 percent so far in August. Much of those gains have come on a few outsized days while other days have seen small incremental gains. Volumes have been light as investors wait for central banks’ meetings next month where policymakers are expected to take action to ease Europe’s debt crisis and boost the economy.