Are we being prudent, precautionary, or both?

The ongoing review conducted by the International Commission on Radiological Protection (ICRP) includes an examination of the ethical foundations of the System of Radiological Protection. ICRP (2018) identified Prudence as one of the four ethical values underpinning the work of the ICRP. In most recent publications, the term regularly appears as a synonym or in conjunction with the Precautionary Principle. However, despite their frequent pairing, the two concepts have distinct meanings and unique histories in ICRP publications. Given the importance of the Precautionary Principle outside of radiological protection, the instability of their relationship can become a serious point of confusion, particularly when more emphasis is placed on protection of the environment. How do we know that we are being prudent, precautionary, or both in our approach to radiological risk assessment and management? This paper examines the definitions and applications of these terms within the ICRP's publishing history. Through a content and semantic analysis of 103 ICRP publications, this study describes their evolution and interrelation, highlights ambiguity and identifies opportunities for further clarification. The ICRP's current review of the System provides a timely opportunity to stabilise the terms, improving a common understanding and, ultimately, the management of radiological risk.