Human languages use complex, structured signals whose meanings are compositional. Recent empirical research has claimed to demonstrate compositionality in bird and primate communication (Berthet et al. 2025; Engesser et al. 2016; Girard-Buttoz et al. 2025; Leroux et al. 2023; Suzuki et al. 2017). While the compositionality of human languages seems beyond doubt, it can be demonstrated powerfully and immediately because of several other important features of language. Clarifying the arguments for compositionality in human languages reveals open questions and alternative hypotheses about the evidence from other species, and directions for further research and possible limitations.
