This paper studies the morphological influence of language contact between Turkic and Tātic language group in Northwest Iran. The postposition under study is the Turkic –inan and how it has entered the morphological system of some Tāti dialects of Iran. In particular, it is shown which Tāti dialects are influenced in this regard and why. The data for this study were collected from interviews with native Tāti and Turkic speakers in Iran and also from descriptive grammars and Tāti-Farsi dictionaries. We have used Narrog's (2010) instrumental semantic map to see which semantic functions are fulfilled with the instrumental-related postposition or case marker in both Tāti and Turkic dialects of Iran and whether they are the same or different in these languages.
