Cognitive psychology and theories of language have had an impact on the development of computer science for many decades.  Early work in cognitive psychology influenced, and was influenced by computer scientists, whilst research on human language has influenced the development of computer languages.  However, there remains a great deal of opportunity for interaction between these disciplines.  This talk will explore how theories of human reasoning developed by cognitive psychologists can shed light on the difficulties people experience in thinking about formal languages in computer science, and hence contribute to reducing those difficulties.  Similarly, ideas from the philosophy of language can help in the development of formal languages.  As illustrations, examples will be drawn from the field of Description Logics.  However, the underlying ideas can be extended to other domains within computer science.