Accentuation tendencies of English.
Various positions of stress in modern English words are due to different origin of the latter. But the freedom of stress in English words is restricted by certain tendencies which make its incidence rather predictable.
The first and the oldest of the English word accentuation tendencies is known as the recessive tendency and the incidence of the main stress in accordance with it is called recessive. The recessive tendency consists in placing the word-stress on the initial syllable. Recessive stress can be of two subtypes:
1) unrestricted recessive stress, falling on the first syllable (ex. 'father, 'mother etc.);
2) restricted recessive stress, falling on the root of words with a prefix, which lost its meaning (ex. be'gin, for'get, a'mong, be'fore etc.).
The recessive tendency is characteristic of all Germanic languages. Throughout the whole historical development of the English language this tendency has always been very strong. Thus, the stress in Anglo-Saxon and Scandinavian polysyllabic derivative words is constant due to the influence of the recessive tendency (ex. 'wonder, 'wonderful, 'wonderfully).
The polysyllabic French words borrowed into English during and after the Norman conquest underwent what is known as accentual assimilation. The stress in them originally fell as in Modern French on the last syllable, but under the strong influence of the recessive tendency it began to shift gradually to the initial syllable (ex. 'colour, 'marriage, 'reason).
The recessive tendency is still felt in Modern English which is especially noticeable in the new borrowings from other languages (ex. 'cosmonaut).
The rhythmic, or rhythmical tendency was caused by the presence in English of a great number of short (monosyllabic and disyllabic) words, many of which are formal words. In a sentence they become unstressed, which creates the rhythm, consisting of alternating a stressed syllable with an unstressed one. The stress determined by the rhythmic tendency is called rhythmical which can be of two subtypes:
1) historically or diachronically rhythmical stress;
2) genuinely, or synchronically rhythmical stress.
Historically rhythmical stress is primary and it falls on the third syllable from the end in three- and four-syllabic words (ex. 'cinema, 'family, ar'ticulate).
The influence of the historically rhythmical tendency was gradual. In borrowed polysyllabic words with the word-final position of primary stress due to the rhythmical tendency there appeared a secondary stress on the syllable separated from the word-final primary stress by one unstressed syllable. These words began to be pronounced in isolation on the model of short phrases in which a stressed syllable alternates with an unstressed one. For some period of time such words had two stresses, but gradually the stress on the last syllable began to weaken because it was contrary to the native English recessive tendency, which caused the strengthening of the secondary stress. When the word-final stress had thus gradually disappeared there remained only one stress on the third syllable from the end of the word. It explains the accentual structure of the overwhelming majority of Modern English words.
The accentuation of words ending in the suffix –ion with its variants –sion, -tion, ation is also rhythmical in origin. Originally the suffix –ion consisted of two syllables, of which the last one bore the accent and was preceded by the unstressed [i]; later, the syllable, preceding [i] due to the rhythmical tendency received rhythmical stress. The last syllable gradually lost its stress with the result that only the rhythmical stress remained. At the same time the unstressed [i] was changed to [j] and in those words in which this [j] was preceded by [s] or [z] it merged with the latter, so that the sounds [∫] and  appeared. This explains the modern pronunciation and the accentual pattern of such words as “nation”, “occasion”, “opinion” etc.
Synchronically rhythmical stress is secondary and it falls on the second pretonic syllable in polysyllabic words, such as “revolution”, “assimilation”, “organization”, “examination”, “pronunciation”, where the primary stress is diachronically rhythmical in nature.
The retentive tendency consists in retaining the stress in a derivative on the same syllable on which it falls on the original word, the word from which the derivative is formed. Although the retentive tendency manifests itself also in the retention of the primary stress of the original word (ex. 'similar, a'ssimilate), much more commonly its manifestation consists in retaining the stress of the original word in the form of secondary stress in the derivative word (ex. 'similar, 'simi'larity).