This paper examines nominalisation in scientific discourse in English, focusing on a distinction between what I will refer to as ‘live’ and ‘dead’ grammatical metaphors. Live metaphors refer to a nominal realisation of an ideational discourse semantic figure; dead metaphors are found in the same nominalisations as live metaphors, but they realise an entity rather than a figure. The distinction is made by drawing on a tristratal approach that is informed by Systemic Functional Linguistics and that considers nominalisation simultaneously from the perspectives of field, discourse semantics, and lexicogrammar. Although the paper focuses on nominalisation, it illustrates a broader line of argumentation that can be extended to the analysis of ideational discourse semantic meanings in general.