How Did Financial-Crisis-Based Criticisms of Market Efficiency Get It So Wrong?

In the aftermath of the financial crisis, market efficiency is being heavily criticized. However, the volatility-based criticisms rely on false grounds as efficiency and speculative bubbles are compatible. Indeed, the efficient market model is about rationality and information, not about stability. This model admits multiple solutions, as do most rational expectations models. One solution is the so-called fundamental one while the others are referred to as rational bubbles. Still, many practitioners, and even some financial academics, keep denying that speculative bubbles are compatible with efficient markets. This paper argues that not only would the recognition of efficient market multiplicity thwart irrationality-based theories, but it would also allow for further empirical developments taking full advantage of the power of diversity. The multiple price dynamics compatible with market efficiency represent a valuable asset largely underestimated by the profession.