In much of the early literature on mechanisms, mechanisms are contrasted explicitly with laws of nature (Bechtel 1988; Bechtel and Abrahamsen 2005; MDC 2000). This contrast clearly grew out of an emerging consensus in philosophy that there are few, or perhaps no, laws of biology (see Section 3.1 above). The empirical generalizations one finds in biology tend to be hedged by ceteris paribus clauses; whether they hold or not depends on background conditions that might not hold and on conditions internal to the mechanism that might fail.  These generalizations, in short, are mechanistically explicable; what necessity they have derives from a mechanism (Cummins 2000; Glennan 1996). Mechanisms thus seem to play the role of laws in the biological sciences: we seek mechanisms to explain, predict, and control phenomena in nature even if mechanisms lack many of the characteristics definitive of laws in the logical empiricist framework (such as universality, inviolable necessity, or unrestricted scope).