Persian dictionaries and grammar books do not agree on the parts of speech of a considerable number of lexical words including infinitives, predicative nouns and adjectives and light verbs of the language and this may cause problems for the learners and the researchers of this language. In the modular grammar approach, language is divided into independent modules which may not correspond in some lexical entries. Based on a study in which words were chosen from Persian dictionaries, books and journals which considered mismatching words, the present paper argues that it is possible to account for the mismatching behaviors of the above groups of Persian words in the framework of modular grammar and terminate the disagreements on the parts of speech of these words.
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