 In the classical Nagelian account (Nagel 1961), reduction amounts to deriving a theory that is to be reduced from a more fundamental reducing theory on the basis of two conditions: deducibility and connectability (see the entry  scientific reduction).  The standard example is the reduction of thermodynamics to statistical mechanics. Nagel thought that from the laws of statistical mechanics one can derive the laws of thermodynamics (deducibility), with the help of “bridge principles” that connect the terms of these two theories (connectability; Nagel 1961: ch. 11; Schaffner 1967). Nagel’s original approach to reduction has been criticized from many angles, but in the present context, the most relevant criticism is that the classical model ignores the distinction between interlevel and intralevel reductions in science (Wimsatt 1976a, 1976b; McCauley 1996). Intralevel (or successional) settings involve competing theories within a particular science and within a particular level, for example the phlogiston theory and the caloric theory of heat. Interlevel settings, on the other hand, involve theories at different levels of organization that thereby have differing explananda, terminology and methodology: for example, cognitive psychology and molecular neuroscience. Nagel’s model in its classic form treats these different contexts equally. Other shortcomings of the Nagelian account are that it only applies to (formalized) theories, ignoring other products of science, and that it fails to incorporate the fact that the reducing theory often corrects the reduced theory (see, e.g., Walter &amp; Eronen 2011). For these and many other reasons, it is widely agreed that the Nagelian model fails to reconstruct reductive relations as they appear in actual science (Wimsatt 1976b, 1979), and that the model in its original form is inapplicable to actual biological cases (Kaiser 2012).