Like many other languages, English has wide variation in pronunciation, both historically and from dialect to dialect. In general, however, the regional dialects of English share a largely similar (but not identical) phonological system. Among other things, most dialects have vowel reduction in unstressed syllables and a complex set of phonological features that distinguish fortis and lenis consonants (stops, affricates, and fricatives). This article describes the development of the phonology of English over time, starting from its roots in proto-Germanic to diverse changes in different dialects of modern English. Abbreviations In the following description, abbreviations are used as follows: Changes by time period This section summarizes the changes occurring within distinct time periods, covering the last 2,000 years or so. Within each subsection, changes are in approximate chronological order. The time periods for some of the early stages are quite short due to the extensive population movements occurring during the Migration Period (early AD), which resulted in rapid dialect fragmentation. Late Proto-Germanic period This period includes changes in late Proto-Germanic, up to about the 1st century. Only a general overview of the more important changes is given here; for a full list, see the Proto-Germanic article. Unstressed word-final and were lost. Early > late PGmc "you carried (sg)". [[Proto-Germanic language#Word-final /m/ > /n/|Word-final became ]]. Word-final was then lost after unstressed syllables with nasalization of the preceding vowel. Hence * > early PGmc > late PGmc > Old English "day (acc. sg.)". The nasalisation was retained at least into the earliest history of Old English. Word-final was lost after an unstressed syllable. This followed the loss of word-final , because it remained before : PrePGmc * > early PGmc > late PGmc "they carried". [[Proto-Germanic language#Unstressed /e/ > /i/| was raised to in unstressed syllables]]. The original vowel remained when followed by , and was later lowered to . Early i-mutation: was raised to when an or followed in the next syllable. This occurred before deletion of word-final ; hence * > early PGmc > late PGmc > German "over". Compare PIE * > early PGmc > late PGmc > German "over". But it occurred after the raising of unstressed to : PIE * > PGmc > "you carry (pl)". This also affected the diphthong , which became . As a consequence of this change, > . The Elder Futhark of the Proto-Norse language still contained different symbols for the