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).
In the following description, abbreviations are used as follows: This section summarizes the changes occurring within distinct time periods, covering the last 2,000 years or so.
Only a general overview of the more important changes is given here; for a full list, see the Proto-Germanic article.
It is unclear if there was ever a distinct "Proto-West Germanic", as most changes in this period were areal, and likely spread throughout a dialect continuum that was already diversifying further.
Thus, this "period" may not have been a real timespan, but may simply cover certain areal changes that did not reach into North Germanic.
This period is estimated to have lasted only a century or so, the 4th to 5th; the time during which the Franks started to spread south into Gaul (France) and the various coastal people began colonising Britain.
Old Frankish (and later Old Dutch) was not in the core group, but was affected by the spread of several areal changes from the Ingvaeonic area.
The following table shows a possible sequence of changes for some basic vocabulary items, leading from Proto-Indo-European (PIE) to Modern English.
For more detail about the changes in the first millennium AD, see the section on the development of Old English vowels.
Prior to that time, both vowels were pronounced the same, as a short vowel /a/; this is reflected by the fact that there is a single merged field corresponding to both Middle English sounds in the Late Old English column (the first column).
However, each vowel has split into a number of different pronunciations in Modern English, depending on the phonological context.
NOTE: In this table, abbreviations are used as follows: 1"Pre-Germanic" in this context refers to a post-PIE language that maintains PIE phonology but with morphological adjustments made as necessary to account for the Proto-Germanic form.
2I-umlaut refers to a sound change that took place around 500 AD with pervasive effects on English vowels.