 The probability skeptic’s ordinary suggestions about how we might be mistaken contrast with the extraordinary possibilities conjured by René Descartes’ skeptic. The Cartesian skeptic tries to undermine vast swaths of knowledge with a single untestable counter-explanation of the evidence (such as the hypothesis that you are dreaming or the hypothesis that an evil demon is deceiving you). These comprehensive alternatives are designed to evade any empirical refutation. The probabilistic skeptic, in contrast, points to a plethora of pedestrian counter-explanations. Each is easy to test: maybe you transposed the digits of a phone number, maybe the ticket agent thought you wanted to fly to Moscow, Russia rather than Moscow, Idaho, etc. You can check for errors, but any check itself has a small chance of being wrong. So there is always something to check, given that the issues cannot be ignored on grounds of improbability.