As is well known, one of the most salient features of English is the great influence of stress on the quality of its vowels. Thus we have the term strong form and weak form, which are used to describe this kind of contextual variation.

Weak form is a common phenomenon in English phonetics. Hence every handbook on English phonetics will devote a separate chapter or section to the subject, or at least will quote a list of weak forms followed by a few comments on their use. For various reasons there are almost as many different lists as there are books on English phonetics. Later we shall see why this must be so. It is not surprising that a pronunciation which never uses weak form sounds very unnatural to English ears and may give the impression that the speaker has a foreign accent even if otherwise s/he has made no mistakes at all. Speakers who are not familiar with the use of weak forms are likely to have difficulty understanding speakers who do use weak forms; since practically all native speakers of British English use them, learners of the language need to learn about these weak forms to help them to understand what they hear. Sometimes it is deemed necessary too to emphasise that weakening the pronunciation of certain words in the proper context is not a sign of careless or vulgar speech and that weak forms are regularly used by educated speakers of the language as well. The reader may feel that native speakers find the speech of foreigners not using those weak forms less clear as they create the impression of focusing too much on words with little information value.

We must distinguish between weak forms and contracted forms. Certain English words are shortened so severely (usually to a single phoneme) and so consistently that they are represented differently in informal writing, e.g. ‘it is’—‘it’s’; ‘we have’—‘we’ve’; ‘do not—‘don’t’.

Almost all the words which have both strong and weak forms belong to a category that may be called function words—words that do not have a dictionary meaning in the way that we normally expect nouns, verbs, adjectives and adverbs to have. Those function words are words such as auxiliary verbs, prepositions, conjunctions, etc., all of which are in certain circumstances pronounced in their weak forms. It is important to remember that there are certain contexts where only the strong form is acceptable, and others where the weak form is the normal pronunciation.

The information on the 38 weak form words introduced in this text is based on English Phonetics and Phonology, A Practical Course by Peter Roach (3rd Edition, C.U.P., 2000)  and the English Pronouncing Dictionary (15^th Edition, C.U.P. edited by Peter Roach and James Hartman.