In this study, corpus method was used to test an assumption of Conceptual Metaphor Theory (CMT) that systematic and conventionally fixed metaphorical expressions have literal meaning in the source domain. The conceptual metaphors LIFE IS A JOURNEY and IDEAS ARE PLANTS were selected for analysis and three keywords from source domain of the metaphors were chosen and matched with their English equivalents. Hamshahri 2 collection of Farsi texts was selected as the corpus of the study. For ease of processing, one third of the corpus comprising of fifty million word tokens was randomly sampled as the working corpus. Collocates of the source-domain keywords, as realizations of fixed metaphoric expressions, were extracted using AntConc software and their concordances were examined. It was found that 1) in conventionally fixed metaphorical expressions, when source-domain keywords were used metaphorically they had collocates that rarely appeared with the same source-domain keywords used literally, and 2) source-domain keywords had gradable degrees of metaphoricity. The findings were interpreted as suggesting that the meaning of fixed metaphoric expressions may not be systematically connected to the metaphor's source-domain meaning.
