In recent years, studies based on Dornyei’s (2005, 2009) L2 motivational self system have focused on the impacts of selves as motivators in second/foreign language learning, but research on the relationship between ideal L2 self and ought-to L2 self is still scant. Therefore, this study aimed to investigate the interrelationship among ideal L2 self, ought-to L2 self, and motivational strength of English learners in Taiwan and the mediation effect of ideal L2 self between ought-to L2 self and motivational strength. A total of 604 Taiwanese university students participated in this study. A questionnaire comprised of three latent variables, ought-to L2 self, ideal L2 self, and motivational strength, was distributed and analyzed using structural equation modeling. The results showed that both ideal L2 self and ought-to L2 self significantly predicted motivational strength, and there was a partial mediation effect with the ideal L2 self as a mediator between the ought-to L2 self and the motivational strength. The findings suggest an alternative explanation that ideal L2 self and ought-to L2 self may not be constructs of the same level, but rather, there is a causal relationship between the two in the cognitive
developmental process.