Lay theories (or ‘implicit theories’) are cornerstones for social cognition: people use lay theories to help them make sense of complex and ambiguous behavior. In this study, we describe recent research on the entity and incremental theories (the belief that personality is fixed or malleable). In so doing, we demonstrate that each theory does not act alone. Instead, each is associated with a set of allied beliefs, the sum total of which cohere into two distinct meaning systems. We present evidence that these meaning systems produce systematic differences in a range of fundamental social cognition processes, with important implications for the field’s understanding of trait/situation attribution, moral judgment, person memory, and stereotyping. We further argue that because meaning systems serve a central meaning-making function, people are motivated to believe that the meaning system they are using is effective and accurate. Accordingly, we present evidence that people exhibit processing distortions and compensatory mechanisms to minimize the impact of information that violates their meaning system. We discuss the implications of these findings for the field’s understanding of basic social cognition.