Bartholomae's law

Bartholomae's law (named after the German Indo-Europeanist Christian Bartholomae) is an early Indo-European (PIE) sound law affecting the Indo-Iranian family. It states that in a cluster of two or more obstruents (stops or the sibilant *s), any one of which is a voiced aspirated stop anywhere in the sequence, the whole cluster becomes voiced and aspirated. Thus to the PIE root *bʰewdʰ- "learn, become aware of" the participle *bʰudʰ-to- "enlightened" loses the aspiration of the first stop (Grassmann's law) and with the application of Bartholomae's law and regular vowel changes gives Sanskrit buddha "enlightened".