Comparative Method

The comparative method systematically compares related languages, or related organisms, to reconstruct a shared ancestor and the changes that separated its descendants. In historical linguistics, where the term is most closely associated, nineteenth-century scholars including Rasmus Rask, Jacob Grimm and later the Neogrammarians compared vocabulary and sound patterns across languages such as Sanskrit, Greek and Latin to reconstruct Proto-Indo-European, a language no text records, on the working assumption that sound change is regular rather than arbitrary. Biology developed a parallel comparative tradition of its own, comparative anatomy, using shared and divergent structures across species to infer common ancestry well before Darwin gave that inference an evolutionary explanation; the two traditions arose largely independently rather than one borrowing the method from the other, though both rest on the same underlying logic of inferring an unobserved common source from patterned similarity and difference among its descendants.