The holist claims that systems of hypotheses, not individual ones, receive evidential support. Particularists claim that systems of hypotheses receive evidential support if and only if each hypothesis in the system does. In the mid-19th century the philosopher John Stuart Mill and the scientist William Whewell debated this issue with respect to the wave theory of light. To believe the theory, Mill said, you must find the ether, which is waving. Whewell replied “not so.” Who was right, and why?