Germanic spirant law

The Germanic spirant law, or Primärberührung, is a specific historical instance in linguistics of dissimilation that occurred as part of an exception of Grimm's law in Proto-Germanic, the ancestor of Germanic languages. The law affects the various series of stops in Proto-Indo-European that underwent Grimm's Law and Verner's Law. If the stops were immediately followed by t or s, they changed to voiceless fricatives (spirants): (/bht/, /bt/, /pt/ >) /pt/ > /ɸt/ (/dht/, /dt/, /tt/ >) /ts(t)/ > /ss/ (/ɡht/, /ɡt/, /kt/ >) /kt/ > /xt/ (/bhs/, /bs/, /ps/ >) /ps/ > /ɸs/ (/dhs/, /ds/, /ts/ >) /ts/ > /ss/ (/ɡhs/, /ɡs/, /ks/ >) /ks/ > /xs/ Under normal conditions, any voiced stop would likely have been devoiced before /t/ and /s/ during Proto-Indo-European times, and so all three Indo-European series of stop consonants (aspirated, voiced and voiceless) had already merged before those two consonants. Therefore, for example, /bht/, /bt/ and /ɡht/, /ɡt/ had already become /pt/ and /kt/ in some of the late Proto-Indo-European dialects. Likewise, /bhs/, /bs/ and /ɡhs/, /ɡs/ had become /ps/ and /ks/. Compare, for example, Latin scribere "to write" and legere "to gather, read" with their past participles scriptus and lectus. Cases before /s/ are also numerous, as can be noticed by comparing Latin scribere and its perfect scripsī, or pingere "to paint" and pinxī and also the genitive noun form regis and its nominative rēx "king". The specifically-Germanic part of the change in which the first plosive became a fricative but not the /t/ following it seems to have been just an exception to Grimm's law. Under the normal operation of the law, voiceless plosives become fricatives in Germanic. However, if two plosives stood next to each other, the first became a fricative by Grimm's law, if it was not so already, but the second remained a plosive. That exception applied not only to series of two plosives but also to series of /s/ and a plosive, and the plosive was then preserved.