Learn etymology · Guide 2 of 3
Sound laws: why sound change is regular
Put English father, foot and fish next to Latin pater, pēs and piscis. Wherever Latin has p, English has f. That is not a coincidence, and it is not three separate accidents. It is one change, which happened once, long ago, to every word that had the sound. Changes like this are called sound laws, and they are the foundation on which all serious etymology is built.
A pattern in the vocabulary
In 1818 the Danish scholar Rasmus Rask noticed that the Germanic languages (English, German, Dutch, the Scandinavian languages and Gothic) differ from Latin, Greek and Sanskrit in a systematic way. In 1822 Jacob Grimm, better known today for the fairy tales he collected with his brother, set the pattern out in full. It became known as Grimm’s law.
The idea is that the ancestor of all these languages, which linguists call Proto-Indo-European, had a set of consonants that Latin, Greek and Sanskrit mostly kept, but which shifted, all together, on the way to Proto-Germanic, the ancestor of English. In the table, the first column is the reconstructed ancestral sound (the asterisk means it is not recorded anywhere, but worked out; bʰ is a b pronounced with a puff of breath).
| Ancestral sound | In Germanic | Outside Germanic | English |
|---|---|---|---|
| p t k became f th h | |||
| *p | f | Latin pēs, ped- | foot |
| *p | f | Latin piscis | fish |
| *t | th | Latin trēs | three |
| *t | th | Latin tenuis | thin |
| *k | h | Latin cornū | horn |
| *k | h | Latin centum | hundred |
| d g became t k | |||
| *d | t | Latin decem | ten |
| *d | t | Latin duo | two |
| *g | k | Latin genū | knee |
| *g | k | Latin grānum | corn |
| bʰ dʰ gʰ became b d g | |||
| *bʰ | b | Sanskrit bhrā́tar- | brother |
| *bʰ | b | Sanskrit bhárati “carries” | bear |
| *dʰ | d | Greek thýra | door |
| *gʰ | g | Latin hostis “stranger” | guest |
The sounds moved like a row of chairs. The plain p t k turned into the hissing f th h; the voiced b d g moved into the empty places and became p t k; the breathy bʰ dʰ gʰ lost their breath and became plain b d g. (The ancestral *b was so rare that good examples are hard to find.)
Some of the most rewarding etymologies fall straight out of the table. Guest and Latin hostis are the same word, from an ancestral *gʰóstis, “stranger”: Germanic made the stranger welcome, and Latin made him an enemy, which is why hostile is a cousin of guest. Corn and Latin grānum (the source of grain) are both “seed”. And hundred and centum (as in century) are, under the layers of change, the same number.
Explaining the exceptions
A law with exceptions is not much of a law. What turned this observation into a science was the discovery that the apparent exceptions have explanations of their own. There are three common kinds.
Borrowings
English paternal, pedal and century keep Latin’s p, p and c. That’s because they were borrowed from Latin in the last thousand years, long after Grimm’s law had run its course. A sound law applies to the words a language had when the change happened, not to words it picked up afterwards. In fact, a word that has not gone through the changes its neighbours have is a sign that it is a later borrowing.
The neighbouring sounds
After an s, the shift didn’t happen: compare Latin spuere with English spew, or Latin stāre with English stand, both with p and t untouched. A sound change can be limited to particular surroundings, and once the surroundings are stated, the law holds again.
Verner’s law: father and brother
The most famous exception was a puzzle for fifty years. By Grimm’s law, the t of Latin pater should give th in Germanic, just as the t of Latin frāter gives the th of Gothic brōþar, “brother”. But Gothic has fadar, “father”, with a d.
In 1875 the Danish linguist Karl Verner found the answer in Sanskrit, which preserves the position of the ancient stress accent. Sanskrit has bhrā́tar-, stressed on the first syllable, but pitár-, stressed on the second. Verner showed that, across the whole vocabulary, the new Germanic f th h (and s) were voiced, becoming d-like sounds, whenever the stress did not fall on the syllable just before them. One word’s exception became a second law. Its traces are still in English: the alternation in was and were goes back to Verner’s law.
Why should sound change be regular?
Sound change is not a change made to words one by one. It is a change in the way a community pronounces a sound, and so it affects that sound wherever it turns up. You can hear the same thing happening in English today. In most of England the r after a vowel has been lost, in car, hard, fort and every other such word, not in a chosen few; most American and Scottish speakers keep it in all of them. Neither group decided this word by word. Over centuries, small shifts like these add up until related languages no longer sound alike at all.
Correspondences, not resemblances
Regularity gives etymologists a test that intuition cannot. English have and Latin habēre mean almost the same thing and look alike, but they are not related: by Grimm’s law, Latin h should not match English h. The word that does fit is Latin capere, “to take”, whose c and p correspond to the h and v of have, just as the table predicts. Look-alikes come about by chance all the time; regular correspondences don’t.
This is also what allows us to work backwards. If the sound changes between an ancestor and its descendants are regular, then comparing the descendants carefully should tell us what the ancestor was like, even if nobody ever wrote it down. That is how proto-languages are reconstructed, and it is the subject of the next guide.