Despite numerous and increasing attempts to define what life is, there is no consensus on necessary and sufficient conditions for life. Accordingly, some scholars have questioned the value of definitions of life and encouraged scientists and philosophers alike to discard the project. As an alternative to this pessimistic conclusion, we argue that critically rethinking the nature and uses of definitions can provide new insights into the epistemic roles of definitions of life for different research practices. This paper examines the possible contributions of definitions of life in scientific domains where such definitions are used most (e.g., Synthetic Biology, Origins of Life, Alife, and Astrobiology). Rather than as classificatory tools for demarcation of natural kinds, we highlight the pragmatic utility of what we call operational definitions that serve as theoretical and epistemic tools in scientific practice. In particular, we examine contexts where definitions integrate criteria for life into theoretical models that involve or enable observable operations. We show how these definitions of life play important roles in influencing research agendas and evaluating results, and we argue that to discard the project of defining life is neither sufficiently motivated, nor possible without dismissing important theoretical and practical research.

Leonardo Bich was supported by grants from the CONICYT, Chile (FONDECYT Regular 1150052), the Basque Government (IT 590-13) and Ministerio de Economía y Competitividad, Spain (FFI2014-52173-P), and a Visiting Fellowship from the Center for Philosophy of Science of the University of Pittsburgh. Revisions were done during Leonardo Bich’s postdoctoral fellowship funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme—Grant agreement no 637647 – IDEM.