Historical linguistics is the study of how languages change through time and how languages are related toeach other . language is always changing . for example the thai language was differrent two hundred years ago from the thai language of today . A thousand years ago it war very different today language . Because language is always changing dialects and different language tend to develop over time from an earlier stage of a language. For example over the past 1,500 years several have developed from Latin including French Spanish portuguese Italian Romanian Catalan and others. Historical linguistics studies these kinds of changes and seeks to explain how and why languages change