This paper studies Persian Idioms. First, based on Nunberg, Sag, and Wasow, the idioms are divided into two groups, namely compositional and non-compositional; then they are studied from cognitive point of view. Metaphor, metonymy, and common knowledge are the main semantic motivations in producing and perceiving idioms. The study concludes that compositional idioms are transparent, while non-compositional idioms are opaque. Furthermore transparent idioms outnumber the opaque ones.
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