conditioned alternation loses the environment that provided the original
Splits are rarer than mergers, and usually arise when a formerly
conditioned alternation loses the environment that provided the original
conditioning, and the previously conditioned alternation becomes two independent
sounds that contrast with each other. This is basically what happened
when /f/ and /v/ split in English ( /v/ having previously
been an alternate of /f/ when /f/ occurred in an intervocalic
position).