Internal Reconstruction

Internal reconstruction is a method of recovering information about a language's past from the characteristics of the language at a later date. Whereas the comparative method compares variations between languages—such as in sets of cognates—under the assumption that they descend from a single proto-language, internal reconstruction compares variant forms within a single language under the assumption that they descend from a single, regular form. For example, these could take the form of allomorphs of the same morpheme.

The basic premise of internal reconstruction is that a meaning-bearing element that alternates between two or more similar forms in different environments was probably a single form in the past, into which alternation was introduced by the usual mechanisms of sound change and analogy.(Deustcher, 2005)

Language forms reconstructed by means of internal reconstruction are denoted with the pre- prefix, similar to the use of proto- to indicate a language reconstructed by means of the comparative method; for example, proto-Indo-European. So, an earlier form of English would be referred to as pre-English, intermediate between hypothetical Proto-Germanic and the earliest attested Old English.

It is even possible to apply internal reconstruction to proto-languages reconstructed by the comparative method. For example, performing internal reconstruction on proto-Mayan would yield pre-proto-Mayan. In some cases it is also desirable to use internal reconstruction to uncover an earlier form of various languages, and then submit those pre- languages to the comparative method. Care must be taken, however, because internal reconstruction performed on languages before applying the comparative method can remove significant evidence of the earlier state of the language and thus reduce the accuracy of the reconstructed proto-language.