In the preceding chapter, I isolated certain conceptual features of the process of theory succession in the physical sciences. I argued there that the key to understanding the relationship between a predecessor theory and its successor lay in the notion of explanation, for the critical test of a successor theory lay in its explanatory strength. In particular, I argued, there is a constraint on any proposed successor theory for a range of phenomena: that its adoption put us in the position of being able to offer explanatory accounts both of the descriptive successes and of some of the descriptive failures (limit conditions) of its predecessor(s). Once this was seen, it became clear, too, that prediction was methodologically ancillary, serving the function of mapping the explanatory boundaries of a pair of theories and thereby establishing the actual empirical situation to answer to the successor, rather than to the predecessor, descriptions. Thus we could account for the fact that a select handful of predictions can do the total confirmatory job.