Prior to the financial crisis most economists, though happily not all, believed in a version of the Efficient Market Hypothesis (“EMH”) which held that financial markets were efficiently and thus always correctly priced. The financial crisis resulted in the EMH being discredited as, despite many warnings, it led central bankers to ignore the threat posed by excess debt and overpriced assets, which believers in the EMH held to be impossible. The original, random walk, form of this hypothesis had been shown to be wrong by the stationarity of stock market returns, but many economists continued to adhere to some version of the EMH. The difficulty in persuading them to discard it was due to a significant degree to the fact that it was seldom enunciated as a well-defined and refutable hypothesis. But value, as generally understood, depends on relative returns and on this basis the EMH, when defined as holding that price and value are the same, is demonstrably wrong. While the EMH was generally understood to be making this claim the imprecision with which it was defined meant that other interpretations were possible, and some economists remain reluctant to drop the idea of efficiency. Continued claims that the market is efficient have produced no hypotheses which are sufficiently well defined to be refutable and they therefore fall on the wrong side of Karl Popper’s famous demarcation between science and nonscience.