 The argument—in whichever direction it is run—is evidently valid, so it remains to consider the premises. There are two main reasons why one might challenge 25. First, one might challenge the left-to-right direction of 25 (from priority pluralism to free recombination) by holding that free recombination is independently blocked. For instance, those who posit brute necessary connections in nature posit such brute necessary connections between the priority pluralist’s basic units of being. Obviously here one enters into deeper issues concerning modality, and the extent to which brute necessary connections are or are not  tolerable.[61]