Stress in English is often said to be “fixed and free”, by which is meant that for each word it is fixed, but that there is no fixed position in the word where it must occur, unlike Czech, Finnish or Hungarian, for instance, where it is invariably on the first syllable of a word, or Polish, where it is (with very few exceptions) on the penultimate.
However, the ‘fixed’ part of this statement has to be hedged around with all sorts of caveats. The stress placement on individual words can change over time,and one of the most frequent complaints made by older people about ‘the young’, is that they mispronounce words by putting the stress in the wrong place.
For most of the twentieth century, there was an argument over the placing of the primary stress in controversy: should it be on the first or second syllable? Advocates of initial stress claim that as it comes from the Latin CONTRA and VERSIA, clearly this is the ‘right’ place to put it. Unfortunately, etymology is never a safe argument to use. If we take the series photograph, photography, photographic, photogravure, the primary stress moves progressively later through the word: first, second, third, and fourth syllable (or, starting from the end: antepenultimate, antepenultimate, penultimate, final), and yet they all begin with the Greek-origin prefix photo-.
Stress has been shifting like this for a very long time. Balcony was, until the middle of the 19th century, stressed on the second syllable. Vagary and quandary were shown in dictionaries until well after the 2nd World War as being stressed on the second syllable, although it is difficult to find even very elderly people who don’t smile if you suggest this pronunciation to them. Decade is another word that has changed: from /ˈdekəd/ in the early 20th century to /ˈdekeɪd/ (my pronunciation) and now more and more often /dəˈkeɪd/
The cases of balcony, vagary and quandary suggest that the Germanic tendency to stress initial syllables is working here, but controversy and decade show an opposite movement – perhaps in these instances treating the first syllable as an unstressed prefix. Integral, /ˈɪntəgrəl/ is also moving to /ɪnˈtegrəl/. Likewise preferable and combatant. Other examples, such as contribute, distribute, may indicate that the Germanic pull is stronger than that of the prefix (initial stress is taking over from the traditional 2nd syllable stress), but if that is so, what are we to make of communal, where second syllable stress is increasing in frequency (the Longman Pronunciation Dictionary gives a ratio of 68% to 32% in favour of initial stress for British speakers, but that was in 1990 – the newest edition repeats the figures, although I suspect, on no evidence apart from my own ears, that it is now nearer 50-50)?
Many nouns are traditionally distinguished from the identically spelt verb by stressing the two differently. For example contrast (initial stress – noun; final stress – verb). But there are also many cases where there is traditionally no stress difference (e.g. practice/practise, where the spelling does not affect the pronunciation; and dispute – 2nd syllable stress in both noun and verb). These patterns are also changing: the dispute type is joining the contrastive stress group (again 68% to 32% preference for the traditional pattern according to LPD), while the contrastive group is losing the contrast by stressing the first syllable in both noun and verb (e.g. import and export).