 Almost all of those pursuing the various metaphors discussed in the previous section embraced a view that had its origins in Descartes, who maintained both non-living and living systems (with the exception of the human mind) operated like machines. But a significant number of researchers rejected this perspective and maintained that living organisms, including cells, are fundamentally different from ordinary physical, mechanical systems. They argued that in one way or another composition from material components is insufficient to account for the phenomena associated with cells. We begin with these opponents of mechanistic conceptions of cells and then examine how those advocating mechanistic approaches responded.