Family relations among languages
Several times in earlier chapters we have compared forms in related languages as evidence that a change has taken place. For example, in Chapter 2, we noted that in Pre-Old English, an /n/ is lost before a fricative, and as evidence we cited a comparison of English goose to German Gans, English tooth to German Zahn, and English five to German fünf. The assumption behind this comparison is that if related languages are different from one another it is because a change has occurred in at least one of them. We are thus assuming that we have a way of knowing that two or more languages are related. And indeed we do. The comparative method is a way of examining the words of two or more languages and determining whether or not they are related and also the nature of the relation.
In this case, by “relation” we mean family relation, as opposed to areal relation, which just means two languages are spoken in geographically contiguous regions. Family relations derive from the common happenstance in which groups of speakers of a single language become separated from one another (usually geographically, by migration) and the language of each group undergoes different changes. At first, the two groups are said to speak different dialects, such as American or British English, because if they got back together they could understand each other. But after a certain time period, say 500 to 1000 years, enough changes would have accrued in both varieties that we have to recognize two different languages. This scenario played out in the territories colonized by the Romans, where Latin was spoken, at first alongside other indigenous languages (e.g. Celtic or Germanic languages), and then replaced or marginalized these languages. Then, for example, the Latin spoken in northern France changed such that it became different from that spoken in southern France. Latin spoken in France changed dramatically, differentiating itself from Latin spoken in Spain and Italy and so on until there are a group of related languages we designate Romance languages. The family relations are called genetic relations and more recently, and perhaps more appropriately, genealogical relations.