English stress can fall on any syllable of a word. This can be seen in the words never, polite and afternoon. However, English stress is not entirely unpredictable. For example, rules can be given for words with penultimate and antepenultimate stress.
Consider the following words: (An Introduction to Phonology: Katamba)
a) cinema Agatha overture Malibu
b) Galapagos America rhinoceros epitome
c) tornado rhododendron aroma bronchitis
The words in (a) and (b) have antepenultimate stress. The ones in (c) have penultimate stress. The difference between the words in (a) and (b) and the ones in (c) is that in (a) and (b) the penultimate syllable is light and in (c) the penultimate syllable is heavy.
The second syllable in cinema consists of a nasal and a schwa. This classifies the syllable as light. Because it is light, it does not bear stress. In the word overture, the second syllable has a schwar or schwa with r-colouring. In many accents of British English, the vowel is not a schwar but rather a vowel similar to the schwa with a longer duration.
The second syllable of tornado consists of a nasal and a diphthong. This classifies the syllable as heavy. For this reason it is stressed. The third syllable of rhododendron consists of a mid front unrounded lax vowel and a nasal. This combination of a vowel and consonant classifies the syllable as heavy. As a result, it carries stress.
Although stress varies in English, it is not entirely random. Rules can be given for English stress. One such rule is the one which determines penultimate and antepenultimate stress in loan words. The rule states that if the penultimate syllable is heavy, it is stressed. On the other hand, if the penultimate syllable is light, stress is then placed on the antepenultimate syllable.