When psychologists test a commonsense (CS) hypothesis and obtain no support, they tend to erroneously conclude that the CS belief is wrong. In many such cases it appears, after many years, that the CS hypothesis was valid after all. It is argued that this error of accepting the "theoretical" null hypothesis reflects confusion between the operationalized hypothesis and the theory or generalization that it is designed to test. That is, on the basis of reliable null data one can accept the operationalized null hypothesis (e.g., "A measure of attitude x is not correlated with a measure of behavior y"). In contrast, one cannot generalize from the findings and accept the abstract or theoretical null (e.g., "We know that attitudes do not predict behavior"). The practice of accepting the theoretical null hypothesis hampers research and reduces the trust of the public in psychological research.