Stability of items: an experimental test

The words of a language are randomly replaced in time by new ones, but long since it was observed that words corresponding to some items (meanings) are less frequently replaced then others. Usually, the rate of replacement for a given item is not directly observable, but it is inferred by the estimated stability which, on the contrary, is observable. This idea goes back a long way in the lexicostatistical literature, nevertheless nothing ensures that it gives the correct answer. The family of Romance languages allows for a direct test of the estimated stabilities against the replacement rates since the protolanguage (Latin) is known and the replacement rates can be explicitly computed. The output of the test is threefold: rst, we prove that the standard approach which tries to infer the replacement rates trough the estimated stabilities is sound; second, we are able to rewrite the fundamental formula of Glottochronology for a non universal replacement rate (a rate which depends on the item), third, we give indisputable evidence that the stability ranking is far to be the same for di erent families of languages. This last result is also supported by comparison with the Malagasy family of dialects. As a side result we also provide some evidence that Vulgar Latin and not Late Classical Latin is at the root of modern Romance languages.