Comparative Method - Demonstrating Genetic Relationship - Application - Step 3, Discover Which Sets Are in Complementary Distribution

Step 3, Discover Which Sets Are in Complementary Distribution

During the late 18th to late 19th century, two major developments improved the method's effectiveness.

First, it was found that many sound changes are conditioned by a specific context. For example, in both Greek and Sanskrit, an aspirated stop evolved into an unaspirated one, but only if a second aspirate occurred later in the same word; this is Grassmann's law, first described for Sanskrit by Sanskrit grammarian Pāṇini and promulgated by Hermann Grassmann in 1863.

Second, it was found that sometimes sound changes occurred in contexts that were later lost. For instance, in Sanskrit velars (k-like sounds) were replaced by palatals (ch-like sounds) whenever the following vowel was *i or *e. Subsequent to this change, all instances of *e were replaced by a. The situation would have been unreconstructable, had not the original distribution of e and a been recoverable from the evidence of other Indo-European languages. For instance, Latin suffix que, "and", preserves the original *e vowel that caused the consonant shift in Sanskrit:

Verner's Law, discovered by Karl Verner in about 1875, is a similar case: the voicing of consonants in Germanic languages underwent a change that was determined by the position of the old Indo-European accent. Following the change, the accent shifted to initial position. Verner solved the puzzle by comparing the Germanic voicing pattern with Greek and Sanskrit accent patterns.

This stage of the comparative method, therefore, involves examining the correspondence sets discovered in step 2 and seeing which of them apply only in certain contexts. If two (or more) sets apply in complementary distribution, they can be assumed to reflect a single original phoneme: "some sound changes, particularly conditioned sound changes, can result in a proto-sound being associated with more than one correspondence set".

For example, the following potential cognate list can be established for Romance languages, which descend from Latin:

They evidence two correspondence sets, k : k and k : ʃ:

Since French ʃ only occurs before a where the other languages also have a, while French k occurs elsewhere, the difference is due to different environments (post-initial a or non-a) and the sets are complementary. They can therefore be assumed to reflect a single proto-phoneme (in this case *k, spelled in Latin). The original words are corpus, crudus, catena and captiare, all with an initial k-sound. If more evidence along these lines were given, one might conclude to an alteration of the original k because of a different environment.

A more complex case involves consonant clusters in Proto-Algonquian. The Algonquianist Leonard Bloomfield used the reflexes of the clusters in four of the daughter languages to reconstruct the following correspondence sets:

Although all five correspondence sets overlap with one another in various places, they are not in complementary distribution, and so Bloomfield recognized that a different cluster must be reconstructed for each set; his reconstructions were, respectively, *hk, *xk, *čk (=), *šk (=), and çk (where ‘x’ and ‘ç’ are arbitrary symbols, not attempts to guess the phonetic value of the proto-phonemes).