01
Regular, Not Random
In 1878 a group of young German scholars, the Junggrammatiker or Neogrammarians, argued that sound change operates without exceptions: when a sound changes in a given position, it changes in every word where that position occurs, across the whole speech community. A change of this kind is called a sound law.
The claim sounds too strong, and in a sense it is an idealisation. But it proved enormously productive. It made historical linguistics testable: a proposed change that works in some words and not in others is not yet understood. Grimm's law, which turned Indo-European *p *t *k into Germanic f þ h (Latin pater, trēs, centum : English father, three, hundred), is the classic example on the Germanic tree.
02
Conditions and Chains
Most sound laws are conditioned. They apply only in a certain environment: at the start of a word, between vowels, before a stressed syllable, next to a particular vowel. The notation used on this site states the change and, where needed, the condition after a slash: k → tʃ / _ i means k becomes ch before i.
Changes also follow one another in time, and their order matters. If s becomes h and later h disappears, a word can lose a sound it never had at the start. Working out the order, the relative chronology, is one of the main ways of dating changes relative to each other. Sometimes changes form a chain, as in Grimm's law, where one series of consonants moves into the slot vacated by another, keeping the old distinctions intact.
03
The Apparent Exceptions
Exceptions are where the interesting discoveries happen. Grimm's law left a set of words where Germanic has d or g instead of the expected þ or h. In 1875 Karl Verner showed that these were regular too: they depended on where the accent fell in the ancestral word, as Sanskrit still shows. Verner's law turned a list of exceptions into a second sound law.
Other exceptions have other explanations. Analogy reshapes words to fit a pattern, as English cows replaced older kine. Borrowing brings in words that never went through the change, which is why English has both native father and Latin-derived paternal. And some words, especially very frequent ones, erode irregularly. The comparative method only works because such exceptions can usually be explained.
04
Comparing Across Families
The same kinds of change turn up again and again in unrelated families: voiceless stops become fricatives, consonants weaken between vowels, final sounds are lost, tones arise from lost consonants. The Sound laws view on this site lines up every sound law in the collection on a single timeline and sorts them by kind of change. The dates are rough midpoints, often uncertain by centuries, and they are there to allow comparison, not as precise chronology.