On the Nagel view, reduction is an interlevel relationship. It is also a relationship between theories. Theories about phenomena at a higher level (e.g., gases, lightning, and life) are reduced to (i.e., derived from) theories about phenomena at lower levels (e.g., molecules, electrons, and physiological systems). Finally, the relationship is formally specified and has little to do with either the content of the theories or the material structures those theories describe. From the mechanistic perspective, each of these features of the Nagel model is problematic.