According to Thomas Jefferson, the ‘constitutional freedom of religion’ is ‘the most inalienable and sacred of all human rights’. But the potentially expansive scope of religious convictions risks making the exercise of that human right controversial. That is because the right is usually taken to offer protection not merely to the holding of particular beliefs, but also to their exercise or manifestation. Such exercise or manifestation may be inconsistent with laws enacted to advance the public interest, or to protect the rights of others. That raises a dilemma: should legal protection for this right be allowed to trump other laws, even if they are in the public interest or seek to protect the rights of others? The project of the thesis is to explore the dilemma of the justification and limits of liberty of conscience (a term that encompasses, but is not limited to, freedom of religion).

In this thesis, I defend the protection of liberty of conscience as against a state’s laws (that is, what are sometimes called ‘exemptions’). Drawing on the ideas of John Rawls – in particular, the concepts of moral personality and the basic liberties – as well as the work of other theorists, I suggest that the right to liberty of conscience is based on recognition respect for people as moral persons who have the capacity for a conception of the good and for a sense of justice. Protection of liberty of conscience is important for the exercise and development of both of these moral powers. Moreover, legal officials, like anyone else, owe duties of respect to the population that should entail respect for their liberty of conscience, and accordingly this explains why government should accommodate this immunity by granting exemptions from the law when needed.

Notwithstanding the respect which is owed, I suggest that the right to liberty of conscience is only one basic liberty among several of equal status. That equality of status results from their similar derivation from the Rawlsian moral powers of a capacity for a conception of the good and for a sense of justice. Accordingly, liberty of conscience is not absolute. Drawing on Rawls, I identify two bases for the defeat of a claim to liberty of conscience: that the exercise of liberty of conscience is incompatible with the basic liberty or liberties of others, in circumstances where the other basic liberty or liberties should be prioritized (compatibility), or that limitation of the exercise of liberty of conscience is necessary in the common interest (necessity). In contrast, ideas of neutrality and dignity, employed by some theorists and courts to assess claims of liberty of conscience, are not relied upon in this thesis.

I then apply the theoretical work undertaken to two case studies involving the limits of claims to liberty of conscience. I first address the theoretical basis of rights to integrity of the person and non-discrimination that are relevant to the case studies, before considering the case studies, which focus on the law of the UK and US. One case study concerns the coronavirus pandemic and objections on the basis of human rights and constitutional law against the enforcement of temporary attendance restrictions on places of worship. The other case study concerns discrimination towards same-sex couples on the basis of religious belief, in contravention of non-discrimination laws. The framework suggests that the claims to liberty of conscience in these case studies should generally fail due to the rights of others and/or the common interest; judicial decisions suggesting otherwise fail to reflect the moral position.