Historical Grammar
No umlaut is possible in sēo niht(night) and sē mōnað (month), plural niht and mōnað (preserved in Mn.E. twelvemonth and fortnight).
The r-Stems contain nouns expressing kinship, and exhibit umlaut of the dative singular.
NOTE.—The N.A. plural is usually the same as the N.A. singular. These umlaut datives are all due to the presence of a former i. Cf. Lat. dative singular patri, frātri, mātri, sorori (<*sosori), and Greek θνϓατρί.
The nd-Stems show umlaut both in then N.A. plural and in the dative singular:
| Sing. N.A. | sē fæðer (father) | sē brōðor (brother) | sēo mōdor (mother) | sēo dohtor (daughter) | sēo swuster (sister) |
|---|---|---|---|---|---|
| D. | fæder | brēðer | mēder | dęhter | swyster |
Loquentes Practice Reference
Our drill practices fæder, mōdor and brōðor. Smith’s r-Stem paragraph gives only the N.A. singular and the umlauted dative singular, and notes that "The N.A. plural is usually the same as the N.A. singular"; the remaining case forms our drill uses follow the a-/ō-declensions as Smith directs in his Summary of O.E. Declensions.