 Matter in motion, by itself, would not seem to have the capacity to produce these results. How could unformed matter become formed? How could the emerging form acquire capacity to function without some vital force or factor that was not strictly material? This was the problem for materialists. Those who began with a materialist metaphysics, assuming that all that can exist is matter in motion, could not see how gradual epigenetic emergence of form could occur. The early modern period brought debates between those who started from metaphysical assumptions of materialism and those who started from epistemological assumptions that empirical observation should provide the basis for scientific knowledge.