Revisiting the seminal studies of attachment formation and reevaluating what it means to become attached

What does it mean to become attached? Three longitudinal studies established the empirical basis for the existing four‐phase model of attachment formation, a model that has remained unmodified and unexamined for over half a century. In this paper, I revisit the research questions, methods, and findings from the seminal studies to reevaluate the current model. The evidence indicates two distinct definitions of attachment onset. In the first two phases of the model, becoming attached is defined by changes in within‐subject behaviors leading to the selection of a discriminated figure. Defined this way, attachment onset is analogous to how bond formation is currently defined in other mammals and how imprinting is understood in birds. In contrast, the third and fourth phases of the model define attachment onset by forming a goal‐corrected relationship. This second definition is human‐centric and relies on secure base behavior as the signature criterion, the same criteria used to classify secure and insecure patterns of attachment. I argue for a narrower definition of attachment by removing goal‐corrected behavior as a criterion and focusing on the normative process of selection. In addition, I integrate contemporary work on pair bonding in humans and other animals to propose new avenues for conceptualizing and studying attachment formation in infancy and beyond in filial and sexual bonds.