The Gricean GCI-PCI divide has long been questioned in linguistic pragmatics. Taking Chinese méimù in the CCL corpus as the case, the present study proposes the cognition-pragmatics diachronic model to examine Grice’s GCI-PCI divide. It is found that with the frequency of repeated usage increasing over time, PCIs develop into GCIs; these two types of conversational implicatures are not easily divided. Semantic change from PCIs to GCIs is a dynamic process of cognition from individual entrenchment to collective conventionalization. By schematization and categorization, the former gradually builds an individual’s knowledge network with many entrenched PCI nodes, while the latter is reflected as sharing some parts of the individual’s knowledge network in the collective minds, i.e., the community’s knowledge network with some conventionalized GCI nodes, further forming socio-cultural conventions in a speech community. During this process, there is a division of labor between context and conventions. Therefore, the diachronic study sheds new light on the relationship between GCIs and PCIs.