Vowel reduction in unstressed syllables is a significant feature of English. Syllables of the types listed above often correspond to a syllable containing a different vowel ("full vowel") used in other forms of the same morpheme where that syllable is stressed. For example, the first "o" in "photograph", being stressed, is pronounced with the vowel, but in "photography", where it is unstressed, it is reduced to schwa. Also, certain common words ("a", "an", "of", "for", etc.) are pronounced with a schwa when they are unstressed, although they have different vowels when they are in a stressed position (see Weak and strong forms in English).