EARLY MODERN ENGLISH ALTERNATION OF /d/ AND /ð/

In Early Modern English, /d/ changed to /ð/ when it followed the major stress and preceded /r/.

For example, OE fæder and modor became EME father and mother, respectively.

This change did not occur in French loanwords or when EME /d/ preceded the suffix -er.

The reverse of this phenomenon also occurred: EME /ð/ sometimes became EME /d/ after /r/ or before /l/. For example, OE morðor "murder" became Shakespearean murther and, finally, PDE murder.