Grassmann's law, named after its discoverer Hermann Grassmann, is a dissimilatory phonological process in Ancient Greek and Sanskrit which states that if an aspirated consonant is followed by another aspirated consonant in the next syllable, the first one loses the aspiration. The descriptive version was given for Sanskrit by Pāṇini.
Here are some examples in Greek of the effects of Grassmann's law:
As the Proto-Indo-European language (PIE) broke up, its sound system diverged as well, as evidenced in various sound laws associated with the daughter Indo-European languages.Especially notable is the palatalization that produced the satem languages, along with the associated ruki sound law. Other notable changes include:
Bartholomae's law in Indo-Iranian, and Sievers's law in Proto-Germanic and (to some extent) various other branches, may or may not have been common Indo-European features. A number of innovations, both phonological and morphological, represent areal features common to the Italic and Celtic languages; among them the development of labiovelars to labial consonants in some Italic and Celtic branches, producing "p-Celtic" and "q-Celtic" languages (likewise "p-Italic" and "q-Italic", although these terms are less used). Another grouping with many shared areal innovations comprises Greek, Indo-Iranian, and Armenian; among its common phonological innovations are Grassmann's law in Greek and Indo-Iranian, and weakening of pre-vocalic /s/ to /h/ in Greek, Iranian and Armenian.
Bartholomae's law, sometimes referred to as the Buddha rule, is a Proto-Indo-European sound law affecting consonant clusters, most clearly in the Indo-Iranian languages. 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 Proto-Indo-European root *bʰewdʰ- 'learn, become aware of', the participle *bʰudʰ-to- 'enlightened' loses the aspiration of the first stop (following Grassmann's law) and with the application of Bartholomae's law and regular vowel changes gives Sanskrit buddha 'enlightened'. The law is named after German linguist Christian Bartholomae, who first described it in 1883.