عنوان مقاله [English]
First the distinctive features of Persian phonological system based on articulatory features have been described,, then the feature specification of 29 Persian phonemes in two tables of consonants and vowels have been presented. In the next section, the theory of feature geometry and such concepts as feature tree and segment trees have been briefly explained. I Introduce two natural segment classes of so called long and short vowels in Persian, i.e. /i α u/ and /e a o/ respectively. Natural segment classes have two characteristics: firstly, that the language has the same behavior with them, and secondly that the number of features necessary to describe each class must be less than the number of features necessary to describe each member of that class. I will show that /i α u/ and /e a o/ are natural segment classes only based on the first characteristics and not the second one. This contradiction may be related to the historical changes of Persian phonological system, in which quantity used to be a distinctive feature, but today it no longer has such a role. I suggest that such classes having one of the two conditions of natural classes, to be called incomplete natural classes.