I looked up the etymology of "father" and see what Etymology Dictionary says:

Old English fæder "he who begets a child, nearest male ancestor;"

It clearly says "fæder" with a D.

Wikitionary also has the D version:

From Middle English fader, from Old English fæder, from Proto-West Germanic *fader, from Proto-Germanic *fadēr, from Proto-Indo-European *ph₂tḗr. Doublet of ayr, faeder, padre, pater and père.

The TH was also D in middle English along with old English.

Also the word "mother":

"female parent, a woman in relation to her child," Middle English moder, from Old English modor

But the word "brother":

Old English broþor, from Proto-Germanic *brothar (source also of Old Norse broðir, Danish broder, Old Frisian brother, Dutch broeder, Old High German bruodar, German Bruder, Gothic bróþar), from PIE root *bhrater-.

I don't know what that is, but it is not D. So the change only took place in some words.

Can anyone explain what kind of change that was and what words it applied to?

  • 1
    Also consider murder, which Shakespeare sometimes spelled murther, and which was originally morþor in Old English. So the sound change from "d" to "th" happened in both directions. Commented Jan 5, 2021 at 13:06
  • @PeterShor - Interesting. Also burden: "Old English byrðen" (etymonline.com/search?q=burden)
    – user387044
    Commented Jan 5, 2021 at 13:17
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    Does this answer your question? /ð/ → /d/ shift in English Commented Jan 5, 2021 at 16:17
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    I don't know whether this is relevant or not, but some tribal languages in northern Kenya distinguish between a normal or 'hard' d sound and a 'soft' d, pronounced by positioning the tip of the tongue between the teeth as if making a 'th' sound. I wonder if this may have been an intermediate stage, or if some of the Old English words spelt with a 'd' were actually pronounced in this way.
    – Nams
    Commented Jan 16, 2021 at 17:39
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    @Nams That seems definitely relevant. The D is normally made at the ridge but when the tongue moves down, it becomes TH. So I think thats what happened gradually in English. In some languages T and D are still made at the teeth (behind the teeth or between but are "plosives" like D and T)
    – user387044
    Commented Jan 17, 2021 at 7:00

1 Answer 1


Grimm's law is at work here.

Grimm's law consists of three parts which form consecutive phases in the sense of a chain shift. The phases are usually constructed as follows:

Proto-Indo-European voiceless stops change into voiceless fricatives. Proto-Indo-European voiced stops become voiceless stops. Proto-Indo-European voiced aspirated stops become voiced stops or fricatives (as allophones). This chain shift (in the order 3,2,1) can be abstractly represented as:

bʰ → b → p → f

dʰ → d → t → θ

gʰ → g → k → x

gʷʰ → gʷ → kʷ → xʷ

Here each sound moves one position to the right to take on its new sound value.

(Source: Grimm's Law at Wikipedia)

Consider the chain shift in bold. This phenomenon is at work in the Latin dental to English tooth and in the examples cited by the OP, from Latin pater to OE fæder to English father.

  • Good Job! I searched on Google but didn't find antything or didn't understand the terminology
    – user387044
    Commented Jan 5, 2021 at 13:14
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    While Grimm's law is relevant, it doesn't answer the question of why mother and father had /d/ in Old English, unlike brother. The Indo-European root had /t/, so Grimm's law implies that Germanic should have had /θ/, not /d/.
    – Colin Fine
    Commented Jan 5, 2021 at 13:21
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    Thanks! BTW, the originators of Grimm's Law are the brothers Grimm (of Grimm's fairy tales fame).
    – rajah9
    Commented Jan 5, 2021 at 13:21
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    Until Middle English (which was long after Grimm's Law operated), fricatives didn't distinguish voicing, so there was no real distinction between /θ/ and /ð/. They were allophones of the same phoneme with variable distribution, like the spellings. The important thing is that the stop changed to a fricative. Commented Jan 5, 2021 at 16:58
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    @Colin Verner's Law explains the change of /þ/ to /đ/ in Proto-Germanic. In West Germanic, all /đ/ became /d/, thus OE fæder.
    – siride
    Commented May 5, 2021 at 23:43

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