a type of consonant attested in no Indo-European language known at the time. The hypothesis was vindicated with the discovery of Hittite, which proved to have exactly the consonants Saussure had hypothesized in the environments he had predicted.

Where languages are derived from a distant ancestor, and are thus more distantly related, the comparative method becomes less practicable. In particular, attempting to relate two reconstructed proto-languages by the comparative method has not generally