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Comparative method

Comparative method (in linguistics)

The purpose of comparative method is to detect historical relationships between languages and to establish a consistent relationship hypothesis by reconstructing:

The essential steps are as follows:

There is, however, a regular correspondence between Latin [d-] and English [t-]:

decem | ten
duo | two
duco | tow
Old Latin dingua | tongue

Closer analysis reveals that the correspondence is both regular and pervasive, and that it is part of a more general regular pattern (Grimm's law)

More trivial equations also hold between Latin and English:

mater | mother
ment- | mind
mus | mouse

They demonstrate that Latin word-initial [m] corresponds to English [m]. However, it is the regularity of the matches, not the identity of sound, that counts here.

On the basis of regular correspondence sets formulate a relationship hypothesis, involving an attempt to reconstruct the hypothetical ancestor of the languages being compared. Without going into detail, Latin [d] and English [t] are both derived from primitive *d (the asterisk means that the sound is inferred rather than historically documented) in the reconstructible common ancestor of both languages (called Proto-Indo-European or PIE for short). We also attempt to recover the past sound changes responsible for the historically known reflexes of the reconstructed protoform. For example (the symbol > should be read as "became"):

PIE *dek^m > Proto-Germanic *texun > Old English teon (attested, yielding Modern English ten)
PIE *dek^m > Proto-Italic *dekem > Latin decem (c = /k/ in Classical Latin)
PIE *dek^m > Proto-Indo-Iranian *daCa > Sanskrit das′a
PIE *dek^m > Greek deka

Each step must be justified, e.g. *k^ > *x (the sound of German ch) is part of a regular pattern seen also in Latin cord- | Germanic *xert- 'heart' (> English heart, German Herz) and many similar equations. The weakening and loss of this *x between vowels in the history of English (*-x- > *-h- > zero) is also regular. So are other changes visible in these word histories, e.g. the development of the syllabic nasal at the end of the word into Greek and Indo-Iranian [a], the change *e > *a (or rather the falling together of *e, *o and *a) in Indo-Iranian, or the so-called Satem development of *k^ in the same group (giving a Sanskrit palatal fricative via an Indo-Iranian palatal affricate).

Regular sound changes form historical sequences and often "feed" one another (an older change creates an environment in which more recent changes apply).

(See also lexicostatistics, August Schleicher and Morris Swadesh)

(See also historical linguistics.)