This chapter makes the case for judicial morality as a safeguard against result-selective reasoning, a decision-making flaw especially pernicious in human rights adjudication. Human rights claims are more value-laden than other judicial work. They can tempt judges to depart from disciplined judging according to the rule of law. One purpose of the rule of law is to constrain discretionary judicial power. Research into the psychology of judging supports the need for constraints. But the legal system affords opportunities – margins of judicial manoeuvre – to engage in result-selective reasoning, from the indeterminacy of human rights texts, the replacement of rules with standards, and the adoption of proportionality analysis. The rule of law’s constraints are not self-enforcing and cannot safeguard against the failure of judges to abide by them. What is required is commitment to judicial morality comprising the modes of judicial responsibility: do no harm, and then, do the right thing, for the right reason, in the right way, at the right time, and in the right words. When judges neglect these moral imperatives, they undermine the quest for consistent adjudication that underpins justice.

The idea of determinatio – first identified and analysed in natural law theory – is crucial for understanding international human rights adjudication. Human rights, as they appear formulated in international human rights treatises and declarations, require specification, implementation, concretisation, i.e., determinatio, at the domestic level. I argue that there are good reasons for this to be so. One such reason is that determinatio allows for the application of a norm to be sensitive to the particular circumstances in which it takes place. Determinatio entails deference in human rights adjudication, the latter being the legal consequence of the reasonable space for discretion granted to states which is entailed by determiatio in international human rights law. Close attention to determinatio allows us to see well-known doctrines of deference (such as the doctrine of the margin of appreciation, of regional consensus and of incrementalism) in a different light—not as concessions to state sovereignty, but as grounded on reasons internal to the legal practice of human rights law, of which determinatio is an integral part.

This chapter presents an overview of the use of proportionality in the case law of the Mexican Supreme Court, which has used it mainly to analyze human rights restrictions established by the legislator in statutes. The study identifies two periods. In the first period, the Court begins to use proportionality to analyze the constitutionality of legislative classifications that allegedly violated the right to equality, under a syncretic methodology that is applied not always consistently. More recently, the test has been used more often and regarding rights of very different types, providing a crucial support to the enforcement of the 2011 human rights’ constitutional amendments. The chapter documents the reception of proportionality in terms of both substance and methodology but also offers insight on the main difficulties experienced along the process and on the challenges its use in the Mexican judiciary poses for the future.