What is called external sandhi, therefore, differs from internal sandhi merely in that the former contains statements which have word juncture as a necessary part of their determining environments, while the latter does not. In some languages, alternants next to word juncture may differ so much from those which are not, and differences determined by word juncture may have so many features in common, that it becomes convenient to arrange all statements involving word juncture environments together. In other languages, however, where many statements apply to environment both within words and across word juncture, it is simpler not to distinguish external from internal sandhi.
- Harris (1942a), Pag. 176