 As noted above, one way in which the attempt to develop a single general model of explanation might fail is that we might conclude that there are causal and non-causal forms of explanation that have little in common. But even putting this possibility aside, another possibility is that explanation differs across different areas of science in a way that precludes the development of a single, general model. It is, after all, uncontroversial that explanatory practice—what is accepted as an explanation, how explanatory goals interact with others, what sort of explanatory information is thought to be achievable, discoverable, testable etc.—varies in significant ways across different disciplines. Nonetheless, all of the models of explanation surveyed above are “universalist” in aspiration—they claim that a single, “one size” model of explanation fits all areas of inquiry in so far as these have a legitimate claim to explain. Although the extreme position that explanation in biology or history has nothing interesting in common with explanation in physics seems unappealing (and in any case has attracted little support), it seems reasonable to expect that more effort will be devoted in the future to developing models of explanation that are more sensitive to disciplinary differences. Ideally, such models would reveal commonalities across disciplines but they should also enable us to see why explanatory practice varies as it does across different disciplines and the significance of such variation. For example, as noted above, biologists, in contrast to physicists, often describe their explanatory goals as the discovery of mechanisms rather than the discovery of laws. Although it is conceivable that this difference is purely terminological, it is also worth exploring the possibility that there is a distinctive story to be told about what a mechanism is, as this notion is understood by biologists, and how information about mechanisms contributes to explanation.