Lesson 3: the comparative method

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.

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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 

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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.