Cowgill's law

Cowgill's law, named after Indo-Europeanist Warren Cowgill, refers to two unrelated sound changes, one occurring in Proto-Greek and the other in Proto-Germanic.

Cowgill's law in Greek
In Proto-Greek, Cowgill's law says that a former vowel becomes  between a resonant  and a labial consonant (including labiovelars), in either order.

Examples:
 * "night" < PIE ' (cf. ', Ved. ' < *nakts, nahts, gen. sg. ' /nekʷts/)
 * "leaf" < PIE ' (cf. ')
 * "mill" < PIE ' (cf. ')
 * "nail" (stem ') < early PG ' < PIE ' (cf. nægl < PGerm ')

Note that when a labiovelar adjoins an affected by Cowgill's law, the new  will cause the labiovelar to lose its labial component (as in ' and ', where the usual Greek change * >  has not occurred).

Cowgill's law in Germanic
Cowgill's law in Germanic has no relation to Cowgill's law in Greek other than having been named after the same person. It says that a PIE laryngeal, and possibly , turns into in Proto-Germanic when directly preceded by a sonorant and followed by. This law is still controversial, although increasingly accepted. Donald Ringe (2006) accepts it; Andrew Sihler (1995) is noncommittal.

Examples are fairly few:
 * Proto-Germanic ' "alive" (whence English quick) < PIE ' (cf. )
 * Proto-Germanic ' acc. du. "us two" (cf. unkis, unc, okkr) < PIE ' (cf. '; Ved. ' acc. du. "us two" < )
 * Possibly tācor "husband's brother" < PIE ' (cf. ', Ved. ', ')

The first two examples, however, have good alternative explanations which don't involve Cowgill's law:
 * Proto-Germanic ' < PIE '.
 * Proto-Germanic ' < PIE ' acc./dat. du. "us two at least" (other accusative personal pronouns may have been built the same way: Proto-Germanic ' acc. sg. "me", ' acc. sg. "you (sg.)", and  acc./dat. du. "you two" ).

If the sound law becomes generally accepted, the relative chronology of this law could have consequences for a possible reconstructed phonetic value of. Since Germanic results from earlier PIE, and since the change occurred before Grimm's law applied (according to Ringe), the resulting change would be actually  >. This would have been more likely if was a voiced velar obstruent to begin with. If was a voiced labiovelar fricative as is occasionally suggested, the change would therefore have been:  >.