 So far, these characterizations suggest that there are just two levels, the level of the mechanism and the level of its components. However, when we take into account that a component can also be mechanism in itself, this picture is expanded into a multilevel hierarchy: The components of that nested mechanism then form a third level, which is two levels lower than the overall mechanism (Bechtel 2008: 147). This mechanistic decomposition can be repeated as many times as necessary; there is no a priori limit to the number of levels in a mechanism. 