Strong evidence for the unity of all the modern Germanic languages can be found in the phenomenon known as the first Germanic sound shift or consonant shift (also called Grimm's law), which set the Germanic subfamily apart from the other members of the Indo-European family. Consisting of a regular shifting of consonants in groups, the sound shift had already occurred by the time adequate records of the various Germanic languages began to be made in the 7th to 9th cent. According to Grimm's law, certain consonant sounds found in the ancient Indo-European languages (such as Latin, Greek, and Sanskrit) underwent a change in the Germanic tongue. For example, the sounds p, d, t, and k in the former became f, t, th, and h respectively in the latter, as in Latin pater, English father; Latin dent, English tooth; and Latin cornu, English horn.
Before the 8th cent. a second shift of consonants took place in some of the West German dialects. For instance, under certain circumstances, d became t, and t became ss or z, as in English bread, Dutch brood, but German Brot; English foot, Dutch voet, but German Fuss; and English ten, Dutch tien, but German zehn. The dialects in which this second consonant shift took place were the High German dialects, so called because they were spoken in more mountainous areas. Standard modern German arose from these dialects. The West Germanic dialects not affected by the second shift were the Low German dialects of the lowlands, from which Dutch and English evolved.
Also peculiar to the Germanic languages is the recessive accent, whereby the stress usually falls on the first or root syllable of a word, especially a word of Germanic origin. Another distinctive characteristic shared by the Germanic languages is the umlaut, which is a type of vowel change in the root of a word. It is demonstrated in the pairs foot (singular), feet (plural) in English; fot (singular), fötter (plural) in Swedish; and Kampf (singular), Kämpfe (plural) in German.
All Germanic languages have strong and weak verbs; that is, they form the past tense and past participle either by changing the root vowel in the case of strong verbs (as in English lie, lay, lain or ring, rang, rung; German ringen, rang, gerungen ) or by adding as an ending -d (or -t ) or -ed in the case of weak verbs (as in English care, cared, cared or look, looked, looked; German fragen, fragte, gefragt ). Also typically Germanic is the formation of the genitive singular by the addition of -s or -es. Examples are English man, man's; Swedish hund, hunds; German Lehrer, Lehrers or Mann, Mannes. Moreover, the comparison of adjectives in the Germanic languages follows a parallel pattern, as in English: rich, richer, richest; German reich, reicher, reichst; and Swedish rik, rikare, rikast. Lastly, vocabulary furnished evidence of a common origin for the Germanic languages in that a number of the basic words in these languages are similar in form; however, while word similarity may indicate the same original source for a group of languages, it can also be a sign of borrowing.
See articles on the individual languages mentioned and on Indo-European.