Isaac Levi is more interested in inquiry and how it progresses than he is in metaphysics. Questions concerning the role of disposition predicates in inquiry are more central to him than those concerning the nature and reality of dispositions. It has not stopped him from giving me and others very useful metaphysical advice. Currently, where empirical metaphysics is in vogue, there is every reason to see whether the two forms of philosophical interest might interlock substantially.

Levi has stimulating ideas indeed on the two forms of philosophical interest, and has recently summarized them in the slogan: “The reality of dispositions is a work in progress” (Levi 2003, p. 152). We can learn much about what kinds of dispositions are acceptable from tracing and comparing the histories of successful and less successful disposition predicates in scientific inquiry.

Levi explores one route along which dispositions become real. His idea is that the introduction of dispositions facilitates covering law explanation by increasing the number of laws. The successful disposition predicate eventually becomes integrated in scientific theory, much like an ordinary theoretical term, whereas the unsuccessful does not. My impression is that Levi thinks that this is the only way a disposition can become real. To evaluate this claim, an alternative course suggested by Jon Elster is introduced. I then try to bring out the differences between Levi's and Elster's views on dispositions, partly by suggesting that they resemble two aspects of full explanations discussed by Wesley Salmon. But more about that below.