Cowgill's law says that a PIE laryngeal , and possibly , turns into in Proto-Germanic when directly preceded by a sonorant and followed by . This law is named after Indo-Europeanist Warren Cowgill.
This law is still controversial, although increasingly accepted. Donald Ringe (2006) accepts it; Andrew Sihler (1995) is noncommittal.
Examples are fairly few:
The first two examples, however, have good alternative explanations which don't involve Cowgill's law:
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: > .