Efficient market hypothesis forms

Is the stock market efficient? Answer in terms of the efficient market hypothesis.

Largely, with caveats. Weak-form efficiency (past prices cannot predict returns) and semi-strong form (public information is priced quickly) are broadly supported for large liquid markets, while strong form (even private information is priced in) fails, since insiders can profit. Known anomalies such as momentum and value, plus limits to arbitrage, suggest efficiency is approximate rather than perfect.