Are Temperament and Personality Traits Sibling Constructs or Twins? Toward a Lifespan Science of Personality Development

Temperament and personality traits both refer to relatively stable individual differences in thoughts, feelings, and behaviors, but they are often studied in isolation from each other. Consequently, there are vast bodies of research exploring the nature, development, and consequences of temperament and personality traits, with little integration between areas. The present study examines the overlap vs. distinctness of temperament and personality traits, with the goal of promoting greater integration. First, we review past theory and research on their connections. Then, we apply 10 criteria from Lawson and Robins’ (2021) sibling constructs framework, supplemented by recently developed methods from large language models, to understand associations at the construct and measurement levels — aiming to orient researchers away from black-or-white thinking that has divided the two fields and toward embracing the complex overlap that characterizes the relationship between these domains. Based on our analyses, we argue that temperament and personality traits show substantial overlap at the construct level, differing mainly in how they are measured. We provide recommendations to unify these unnecessarily disparate literatures, paving the way toward a genuine, integrated science of personality development across the lifespan.