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 from Late Proto-Germanic to Old English

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.

Northwest Germanic period

This was the period after the East Germanic languages had split off. Changes during this time were shared with the North Germanic dialects, i.e. Proto-Norse. Many of the changes that occurred were areal, and took time to propagate throughout a dialect continuum that was already diversifying. Thus, the ordering of the changes is sometimes ambiguous, and can differ between dialects.

West Germanic period

This period occurred around the 2nd to 4th centuries. 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 ends with the further diversification of West Germanic into several groups before and during the Migration Period: Ingvaeonic, Istvaeonic (Old Frankish) and Irminonic (Upper German).

Ingvaeonic and Anglo-Frisian period

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. Changes in this period affected the Ingvaeonic languages, but not the more southerly Central and Upper German languages. The Ingvaeonic group was probably never homogeneous, but was divided further into Old Saxon and Anglo-Frisian. 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 Anglo-Frisian languages shared several unique changes that were not found in the other West Germanic languages. The migration to Britain caused a further split into early Old English and early Old Frisian.

Old English period

This period is estimated to be c. AD 475–900. This includes changes from the split between Old English and Old Frisian (c. AD 475) up through historic early West Saxon of AD 900:

Changes by time period from Middle English to American-British split

The Middle English Period

This period is estimated to be c. 900–1400.

Up to Shakespeare's English

This period is estimated to be c. AD 1400–1600.

Up to the American–British split

This period is estimated to be c. AD 1600–1725.

Changes by time period from after American-British split to after World War II

After American–British split, up to World War II

This period is estimated to be c. AD 1725–1945.

After World War II

Some of these changes are in progress.

Examples of sound changes

The following table shows a possible sequence of changes for some basic vocabulary items, leading from Proto-Indo-European (PIE) to Modern English. The notation ">!" indicates an unexpected change, whereas the simple notation ">" indicates an expected change. An empty cell means no change at the given stage for the given item. Only sound changes that had an effect on one or more of the vocabulary items are shown. NOTE: Some of the changes listed above as "unexpected" are more predictable than others. For example:

Summary of vowel developments

Development of Middle English vowels

Monophthongs

This table describes the main historical developments of English vowels in the last 1000 years, beginning with late Old English and focusing on the Middle English and Modern English changes leading to the current forms. It provides a lot of detail about the changes taking place in the last 600 years (since Middle English), while omitting any detail in the Old English and earlier periods. For more detail about the changes in the first millennium AD, see the section on the development of Old English vowels. This table omits the history of Middle English diphthongs; see that link for a table summarizing the developments. The table is organized around the pronunciation of Late Middle English c. 1400 AD (the time of Chaucer) and the modern spelling system, which dates from the same time and closely approximates the pronunciation of the time. Modern English spelling originates in the spelling conventions of Middle English scribes and its modern form was largely determined by William Caxton, the first English printer (beginning in 1476). As an example, the vowel spelled ⟨a⟩ corresponds to two Middle English pronunciations: in most circumstances, but long in an open syllable, i.e. followed by a single consonant and then a vowel, notated aCV in the spelling column. (This discussion ignores the effect of trisyllabic laxing.) The lengthened variant is due to the Early Middle English process of open-syllable lengthening; this is indicated by (leng.). Prior to that time, both vowels were pronounced the same, as a short vowel ; 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, this earlier Middle English vowel is itself the merger of a number of different Anglian Old English sounds: Moving forward in time, the two Middle English vowels and correspond directly to the two vowels and, respectively, in the Early Modern English of c. 1600 AD (the time of Shakespeare). However, each vowel has split into a number of different pronunciations in Modern English, depending on the phonological context. The short, for example, has split into seven different vowels, all still spelled ⟨a⟩ but pronounced differently:

Diphthongs

This table describes the main developments of Middle English diphthongs, starting with the Old English sound sequences that produced them (sequences of vowels and g, h or ƿ) and ending with their Modern English equivalents. Many special cases have been ignored.

Development of Old English vowels