Transcendental arguments have gained a lot of attention over the past twenty years, mainly in the field of theoretical reason. Yet few scholars have looked at their relevance to practical reason. Christian Illies argues that although this methodological avenue is not yet well-paved, transcendental arguments have great potential in ethics, as they promise rational justification of normative judgements.There are two main types of transcendental argument that have been developed for this purpose in recent years. One is based on an analysis of the implications of agency (mainly by Alan Gewirth), the other on an analysis of reason as a discursive process with normative presuppositions (Karl-Otto Apel and other continental philosophers, but also Onora O'Neill). Illies finds that these arguments have severe limitations, and argues that practical reason should involve a different analysis: judgement formation must be analysed as a form of agency. Once this starting point is secured, by showing that it cannot rationally be denied, then two things can be transcendentally inferred: first, that there exists a categorical demand upon agents to arrive at true judgements, and second, that we must respect freedom of agency in general. Here our ordinary notions of right and wrong find secure ground. Compelling and original, The Grounds of Ethical Judgement offers ample evidence that transcendental arguments may provide long-sought foundations for morality.