Robert J. Geller et al. are on shaky ground when they state, in the title of their Perspective (1), that earthquakes cannot be predicted. In spite of their advice, we should not stop studying the physics of preparation for catastrophic rupture, in the field, the laboratory, and theoretically; neither should we stop measuring crustal parameters that might furnish constraints for physical models; and we should continue researching statistical methods to evaluate prediction claims and to test hypotheses quantitatively. Some of the arguments Geller et al. put forward are incorrect. For example, the " slip on geological faults " is not always as " sudden " as they state. In 10% to 30% of large earthquakes, foreshocks occur days (2) to months (3) before the main shock. Seismol-ogists agree that foreshocks are a symptom of some preparatory process to the main rupture. Thus, foreshocks are precursors. If that process could be detected and understood by measuring the several physical parameters of Earth's crust that probably change during it, then prediction would be possible, even if foreshocks themselves can be identified with a low probability only (4). When Geller et al. state that " [t]here are no objective definitions of 'anomalies' " and that " statistical evidence for a correlation is lacking, " they appear to be referring to specific papers that have been criticized (5). However, there are examples of clearly formulated , even tested, hypotheses. Evison and Rhoades (6) formulated a rigorous statistical test and applied it in real time to their well-defined hypothesis of precursory earthquake swarms. The algorithm M8 (7) has been tested in real time, and critically evaluated by others (8). The hypothesis of precursory quiescence also has been clearly stated (9), and specific predictions have been made to test it (10). On the basis of a mathematical model of failure of earth materials , the hypothesis of increasing moment release has been formulated (11) and tested by predictions (12). Geller et al. are also incorrect in stating that " no quantitative physical mechanism links the alleged precursors to earthquakes. " Laboratory rock fracture experiments have shown that dilatancy occurs in rocks under high deviatoric stresses and that rock properties are drastically altered by this phenomenon (13). Dilatancy could explain many precursors, as proposed by Scholz et al. (14). An alternate mechanism to explain precursors is a reduction in ambient stress level that results from strain softening …