This paper examines the hypothesis that all public policies are based, at least in part, on rhetorical strategies. By analysing public policies implemented in the context of sustainable development, this article emphasises the need for and the challenges of providing legitimate foundations for the rhetorical means used to encourage change; it is these foundations that determine a given policy's effectiveness. To do so, historical analyses are used, as well as socio-economic perspectives examined through textual analysis. The text concludes by showing the importance of a common framework for action based on shared values at the regional level for legitimising the political use of rhetoric to change behaviours and attitudes.