<p>Abstractness — the capability to form and use abstract concepts, like ‘fantasy’ — is pivotal to human cognition. Different abstract concepts are characterized by different degrees of sensorimotor, interoceptive, emotional, linguistic and social aspects. In this Perspective, we propose a social route to abstractness, highlighting the role of social interaction and conceptual flexibility in abstract concept acquisition and use. We distinguish two notions: ‘socialness’, the idea that the content of abstract concepts evokes more social aspects than concrete concepts, and ‘social metacognition’, a process that includes a monitoring and an interactive phase. Compared with concrete concepts, social support is more critical to acquiring abstract concepts and to aligning and co-building conceptual meaning while using them. We also introduce a semantic dimension, vagueness, which distinguishes abstract concepts with more determinate meaning (such as some scientific and magnitude concepts) and abstract concepts whose meaning remains vague and socially negotiable. We connect the literatures on concepts, knowledge outsourcing and knowledge communities and highlight open research questions to test the social route to abstractness.</p>