This study, based on Conceptual Blending Theory, finds that "could" integrates connotations of "can" both as a modal verb and as a past tense form. The blending process involves three domains, namely, Society, Cognition and Speech Act. In the Society domain, "could" denotes the likelihood of a certain action or state due to the ability or quality of people or objects. In the Cognition domain, "could" means it is less likely that the speaker, whether he has the ability or quality, will conjecture or presume a certain action or state at the point of speaking. In the Speech Act domain, "could" indicates indirectness and politeness when the speaker asks the listener to perform a certain act. In addition, "could" is also explored from other perspectives.