Grassmann's Law is a rule of phonology in Ancient Greek and Sanskrit which states that if an aspirated consonant is followed by an aspirated consonant in the next syllable, the first one loses the aspiration. Grassmann's Law was known to the ancient Sanskrit grammarians (about 500 B.C.), but its common name in Western linguistics honors the first European linguist to explicate the phenomenon, Hermann Grassmann.

Here are some examples in Greek of the effects of Grassmann's Law:

• [t^hu-o:] θυω 'I kill an animal'
• [e-tu-t^he:] ετυθη 'it was killed'

• [t^hrik-s] θριξ 'hair'
• [trik^h-es] τριχες 'hairs'

• [t^hap-sai] θαψαι 'to bury-aorist'
• [tap^h-ein] ταφειν 'to bury-present'

In the reduplication which forms the perfect tense in both Greek and Sanskrit, if the initial consonant is aspirated, the prepended consonant is unaspirated by Grassmann's Law. For instance [p^hu-o] φυω 'I grow' : [pe-p^hu-ka] πεφυκα 'I have grown'.

Grassmann's Law does not apply in other Indo-European languages, such as Latin. The perfect tense of facere "make", for instance, is f^hef^haked in Old Latin (fecit in Classical - the reduplication was lost).

Diaspirate roots

Cases like [t^hrik-s] ~ [trik^h-es] and [t^hap-sai] ~ [tap^h-ein] illustrate the phenomenon of diaspirate roots, for which two different analyses have been given.

In one account, the "underlying diaspirate" theory, the underlying roots are taken to be /t^hrik^h/ and /t^hap^h/. When an /s/ (or word edge, or various other sounds) immediately follows, then the second aspiration is lost, and the first aspirate therefore survives ([t^hrik-s], [t^hap-sai]). If a vowel follows the second aspirate, it survives unaltered, and therefore the first aspiration is lost by Grassmann's Law ([trik^h-es], [tap^h-ein]).

A different analytical approach was taken by the ancient Indian grammarians. In their view, the roots are taken to be underlying /trik^h/ and /tap^h/. These roots persist unaltered in [trik^h-es] and [tap^h-ein]. But if an /s/ follows, it triggers an "aspiration throwback", in which the aspiration migrates leftward, docking onto the initial consonant ([t^hrik-s], [t^hap-sai]).

Contemporary scholars are divided on which of these approaches is correct. The linguist Ivan Sag has pointed out an advantage of the ancient Indian theory, namely that it explains why there are no patterns like hypothetical "[trik-s] ~ [trik^h-es]". The underlying-diaspirate theory incorrectly predicts that these should occur.

Reference

• Sag, Ivan. A. (1974) "The Grassmann's Law Ordering Pseudoparadox," Linguistic Inquiry 5, 591-607.