This article discuss the notion of effectiveness by employing a critical theory understanding of rationality, which recognizes three different types: cognitive–instrumental, moral–practical and aesthetic–expressive. This distinction is important for understanding effectiveness
in environmental assessment. Furthermore, such understanding has to do with whether impact assessments can protect environmental values or not. Both terms – rationality and effectiveness – are frequently and vigorously used in theory and discussion on environmental assessment practice
and development; they are also widely used synonymously, albeit often unconsciously. In outlining such confusion, the article also discusses so-called post-rational approaches to environmental assessment. Finally, from these theoretical clarifications and detailing of concepts the implications
for environmental assessment practice are outlined.