A vowel shift is an overall change in the inflection or phonetics of a vowel sound over time, in a particular language. A vowel shift can apply to any language, but some are more vulnerable to this kind of change than others. Generally, a vowel shift happens over a significant period of time, usually hundreds of years, according to a shared dialect that develops gradually, and which includes more and more speakers until it naturally becomes a widespread, standard feature of the language. This kind of change is a prominent aspect of the field of historical linguistics.
Every language experiences vowel shifts that linguists look at in their overall study of the evaluation of the language, and its relationship with other nearby languages. For example, in the English language, experts have identified a “great vowel shift” that happened over a span of three centuries, from about the middle of the 15th century to the middle of the 18th century. Other smaller shifts have occurred in the English language, but many linguists study the great vowel shift, and similar shifts in other languages, to understand how languages mutate over time. Historic vowel shifts are most commonly identified by studying changes in the way that words are spelled over time; what initially may appear to be spelling mistakes by scribes will slowly morph into common usage.
Linguists can also benefit from knowing the entire history of a language when they look at vowel shifts and other dynamic changes. Taking the example of English again, historians can see how the language began with old English, which had its own set vowel sounds, and changed into more modern versions. Even today, linguists are looking at current changes, for example, in American English, where experts have identified a pattern that they are calling a major vowel shift in the northeastern U.S. Experts are calling this the “northern cities shift,” and it has been covered on major media outlets, as well as in scholarly articles.
In vowel shifts, vowels change their sound in a number of ways. One of the most common ones is when a vowel becomes diphthonged. A diphthong is a vowel sound that has two separate components; for example, in English, the dipthong “oy” has a distinct ‘o’ and ‘ee’ combination. Vowels that become diphthonged are generally more drawn out, though that’s not necessarily always the case. A vowel may become either longer or shorter, and may even mutate into a completely different vowel sound altogether.
Scientists have found that vowel shifts, together with consonant shifts, are largely social, and that there is an organic social process driving the most broadly defined shifts. Linguists sometimes use Venn diagrams, or similar visual tools, to observe the precise ways that a set of individuals pronounce their vowels. Some experts theorize that some vowel shifts and other dialect changes may relate to social mobility, as people from different linguistic groups encounter and influence one another. For example, the Mongolian-Tatar invasion of Russia in the 13th century is thought to have heavily influenced the development of Russian, causing it to diverge significantly from other Slavic languages.
In general, mass media tends to produce a ‘standardization’ of vowel sounds within a language by building a defined common accent for a large region. Many of those familiar with vowel shifts, hold that these language changes thrive despite any attempts at standardization, largely through their natural origin in communities, where individuals influence one another’s dialects and speech patterns to a high degree. Theorists often try to understand vowel shifts within the general observation of ‘natural language’ and local dialect.