Nasal vowels

Whether and to what extent this distinction was phonemic is a matter of debate. Phonemic nasal vowels definitely occurred in Proto-Norse and Old Norse down to at least 1125 AD, the earliest possible time for the creation of the First Grammatical Treatise (which documents nasal vowels). Surface (possibly phonemic) nasal/non-nasal contrasts occurred in the West Germanic languages down through Proto-Anglo-Frisian of 400 AD or so.

There are apparent examples indicating that phonemic nasality must have occurred at some stage of Proto-Germanic, e.g. the three-way distinction of final -u/-ũ/-un in *fehu "livestock" vs. *nahtũ "night (acc.)" vs. *tehun "ten". Since final -ũ comes from earlier -un while final -un comes from earlier -unt, it could be claimed that Proto-Germanic actually had an underlying phonemic contrast -u/-un/-unt and that the development of phonemic nasality occurred only after Proto-Norse split off. This makes it hard to account for the relative chronology of sound changes, however. The process of nasalisation must have occurred before the loss of word-final -t, because from earlier -nt, -n remained in the 3rd person plural ending, and also some numerals. And that change in turn must have preceded the loss of word-final -a and -e, because earlier -ta remained as -t in the 2nd person singular past ending of strong verbs. Both of these changes were universal in Proto-Germanic and there are no daughter languages that were unaffected. Therefore the analysis with word-final nasal vowels is most likely to be correct.

Later developments

Due to the emergence of a word-initial stress accent, vowels in unstressed syllables were gradually reduced over time, beginning at the very end of the Proto-Germanic period and continuing into the history of the various dialects. Already in Proto-Germanic, word-final /e/ and /ɑ/ had been lost, and /e/ had merged with /i/ in unstressed syllables. Vowels in third syllables were also generally lost before dialect diversification began, such as final -i of some present tense verb endings, and in -maz and -miz of the dative plural ending and 1st person plural present of verbs.

Word-final short nasal vowels were however preserved longer, as is reflected Proto-Norse which still preserved word-final -aN (horna on the Gallehus horns), while the dative plural appears as -mz (gestumz on the Stentoften Runestone). Somewhat greater reduction is found in Gothic, which lost all final-syllable short vowels except u. Old High German and Old English initially preserved unstressed i and u, but later lost them in short-stemmed words and then in many long-stemmed ones as well.

Old English shows indirect evidence that word-final -aN was preserved into the separate history of the language. This can be seen in the infinitive ending -an (< *anaN) and the strong past participle ending -en (< *-anaz). Since the early Old English fronting of /ɑ/ to /æ/ did not occur in nasalized vowels or before back vowels, this created a vowel alternation because the nasality of the back vowel aN in the infinitive ending prevented the fronting of the preceding vowel: *-anaN > *-an, but *-anaz > *-ænæ > *-en.

Morphology

Historical linguistics can tell us much about Proto-Germanic. However, it should be kept in mind that these postulations are tentative and multiple reconstructions (with varying degrees of difference) exist. All reconstructed forms are marked with an asterisk (*).

Simplification of the inflectional system

It is often asserted that the Germanic languages have a highly reduced system of inflections as compared with Greek, Latin, or Sanskrit. Although this is true to some extent, it is probably due more to the late time of attestation of Germanic than to any inherent "simplicity" of the Germanic languages. As an example, there are less than 500 years between the Gothic Gospels of 360 AD and the Old High Germanic Tatian of 830 AD, yet Old High Germanic, despite being the most archaic of the West Germanic languages, is missing a large number of archaic features present in Gothic, including dual and passive markings on verbs, reduplication in Class VII strong verb past tenses, the vocative case, and second-position (Wackernagel's Law) clitics. Many more archaic features may have been lost between the Proto-Germanic of 200 BC or so and the attested Gothic language. Furthermore, Proto-Romance and Middle Indic of the fourth century AD—contemporaneous with Gothic—were significantly simpler than Latin and Sanskrit, respectively, and overall probably no more archaic than Gothic. In addition, some parts of the inflectional systems of Greek, Latin, and Sanskrit were innovations that were not present in Proto-Indo-European.