Chapter 4 explores mood systems and structures. It concentrates on paradigmatic relations – and the ways in which these can be motivated in the grammars of English, Spanish and Chinese. This chapter foregrounds questions about the nature of functional language typology, when confronted with the diverse structural realisations of mood in three different languages. It highlights the need to focus on system rather than structure, on higher ranks rather than lower ones and ultimately on discourse semantics rather than grammar by way of establishing comparable ground whenever languages are being contrasted and compared.