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vocabulary is the same in all languages. Fourth, if we know the percentage of true
cognates within the basic vocabulary between a pair of languages, we can calculate the
length of time that has elapsed since the two languages began to diverge from a single
parent language.
Bennett & Sterk (1977) are concerned about the use of lexicostatistics to identify
lower-level branching in a genetic tree. They state:
Lexicostatistics, while useful for preliminary gross subgrouping, is not—if used
alone—adequate for indication of fine degrees of relationship. The nature of
lexicostatistics is such that geographic and social proximity tends to increase
cognacy scores significantly. (p. 245)
In addition, many scholars question the basic assumptions of lexicostatistics. For
example, Dixon (1997) states, “The rate at which a language changes is not constant and
is not predictable” (p. 9). He then gives examples of languages with accelerated change.
He also states, “There is no universal principle that core vocabulary...is less likely to be
borrowed than non-core items” (p. 10). He states that in Australia, the percentage of
shared vocabulary between a pair of languages is the same regardless of the number of
items compared. So while lexicostatistics may be useful as a rough estimate, the accuracy
of the method is in serious doubt.
3. Shared innovations. Evidence from shared innovations has been used, often in
conjunction with lexicostatistics, in order to justify certain nodes in a classification. It is
assumed that if a language produces an innovation at a certain point in time, then all the
descendents of that language will have that form whereas all externally-related languages
will not.
This of course runs the risk of skewing due to borrowings, chance or symbolism,
just as in the method of resemblances and lexicostatistics. Williamson (1989b: 249)
points out another problem: “There is a certain problem in the use of lexical innovations
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