This article explores the notion of sound judgement by citizens in environmentally attentive democracies. The argument is against indoctrination, and in favour of greater continuity and progression throughout all phases of education. A democratic education that is attentive to issues of environmental sustainability will need to draw on the evidence base of science. This is necessary but not sufficient. Learners need to be able to synthesise understanding from a range of disciplines, including those that address questions of value and judgement. Knowledge and understanding alone do not necessarily lead to a commitment to action for sustainability, and this can result in temptations to take short cuts that result in pupils making rhetorical commitments. The paper looks to the liberal educational philosophy of Paul Hirst as a basis for curriculum analysis and argues that the ability to synthesise an understanding of environmental and sustainable development issues from the irreducible forms of knowledge proposed by Hirst is an advanced skill that requires development over a protracted period.