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particularly of the ages of language families without documented histories.
The basic premise of glottochronology is the fact that the basic vocabulary of
human language tends to be replaced at a constant rate throughout its development.
This approach is based on the principle stated by E. Sapir who said that the
greater the degree of linguistic differentiation within the group, the greater was the
period of time that must be assumed for the development of such differentiation.
If we could measure the degree of differentiation of two related languages, this
would show the relative Length of time that they had been diverging from their
common ancestor: it would be glottochronology (from Greek
glotta
"language" and
chronos
"time").
The glottochronological method involves three principle variables: the rate of
retention, the period of time and the proportion of coinciding test list equivalents in
two languages that are related.
The formula for finding the rate of retention is t=log c ^ log r in which t=the
period of time between two stages of a language, c=the proportion of common forms,
and r=the rate of retention. With this formula, it was found that the rate of retention is
approximately 80 per cent per thousand years.
Glottochronology is the study of the rate of change in language, and the use of
the rate for historical inference, especially for the estimation of the age of a language
and its use to provide a pattern of internal relationships within a language family.
In principle, glottochronology should be applied only after the comparative
method has prepared the ground, and it is of use mainly for languages with long
historical stages of more than a thousand years.
Even in ideal conditions, glottochronological dates provide only a rough
estimate of the most probable date when the related languages diverged. Practically,
different investigators give different data for the divergence dates of linguistic families.
M.Swadesh, an American linguist who supports this method passionately, gives, for
example, a time depth of 46 centuries since the minimum divergence between Aleut
and south-west Greenlandic, considering this a unit of the fullest divergence in the
family. The exact calculation depends on many factors, such as, for example,
differences in the judgment of cognates, differences in the material selected from
within a family, etc.
Thus, the divergence times revealed by the glottochronological method are not
all accepted, since the use of this method has not been generally recognized. Beyond
this, we may consider comparable those divergence times in which we have a good
deal of confidence, and our degree of confidence must depend upon the circumstances.
We can be more confident in divergence times that are confirmed by evidence from
other sources. Swedish was quite right when he wrote:
"Lexicostatistical data must be coupled with other evidence, including that of
archaeology, comparative ethnography, and linguistic paleontology. The separate lines
of study serve to verify or correct one another and to fill in details of the story."
Many linguists attack glottochronology for basing itself on the false premise that,
when languages begin to diverge, -the separation is sharp and complete. Besides, it is
doubtful whether the vocabulary of one language family changes at the same rate as
that of another. What has been established for Indo-European languages cannot
necessary be applied to other families? Then again, one should bear in mind that the
test list of words taken for statistical calculation includes items of vocabulary which
have been subject to various cultural influences. We must be very careful in the
application of mathematical techniques to the measurement of linguistic change.
Some of them must be abandoned as groundless.
Only the comparative method that emerged at the beginning of the 19th
century, now coupled with other methods which, taken together, help to penetrate
deeper into the prehistoric past of the Indo-European languages, can be considered a
really sound approach to the understanding of the history of language.
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