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Background: Recent scholarship has identified the risks associated with various scenarios (climate change, pandemics, nuclear war, and artificial intelligence) as imposing greater threats to the future of humanity than any previous risk (Ord, 2020), spurring recent efforts by lawmakers to draft provisions covering scenarios involving such “existential risks.” Across the world’s jurisdictions, judges (whether by tradition or by law) tend to interpret legal provisions according to their ordinary meaning (i.e., as they’re ordinarily understood by laypeople).

Methods: Across 4 studies (n~7,000), we investigate ordinary people’s interpretation of existential risk (a) as compared to related terms in the catastrophic risk and legal literature; (b) with and without an accompanying technical definition; and (c) as applied to concrete scenarios of varying degrees of expected harm.

Results: We find that ordinary people’s interpretation of existential risk (a) like the technical meaning, is narrower than that of other terms in the legal and catastrophic risk literature; (b) is mostly unaffected by the presence of a definition, except in cases when the definition contains an explicit probability threshold; (c) mostly, though not entirely, resembles an expected harm calculation; and (d) differs widely between abstract and concrete scenarios but is mostly stable across concrete scenario type (e.g. AI, pandemics).

Implications: These findings provide critical insights both for lawmakers drafting existential risk legislation and for judges tasked with interpreting and applying this legislation, as well as new insight into the coherence and justification of the ordinary meaning principle more generally. This study also lays the foundation for a new research program we refer to as “ex ante ordinary meaning analysis”—focused not only on how judges can and should interpret legal provisions, but on how lawmakers can and should draft legal provisions so as to best achieve their policy aims.