The question what is emotion? has long been at the core of theoretical debates. The IAC-E is a useful framework for understanding relationships among responses in emotional situations. However, this approach cannot address the nature of emotion. Researchers determine what counts as emotion in the IAC-E, and this decision impacts the relationships detected and inferences made. The assumptions of researchers about emotion change the output. Further, the model is not theoretically agnostic and is best suited to examine emotion perception/knowledge, as in the simulations presented. According to some theories, experienced emotion is qualitatively different than situations that involve perceiving others' emotion or semantic knowledge. Addressing the nature of emotion requires empirical examination of the assumptions made in each theory.