It was the Church's public presence, its outward-facing ministry, Combes could not and did not abide — precisely what Lamennais had shrewdly realised any defence of religious liberty needed to cover.

This time the Church was ready to learn from losing. The paradigm shift really begins with the remarkable pontificate of Leo XIII (1878-1903). The rise of the nation state, and then its turn against Catholicism, caused Leo fundamentally to rethink the freedom of the Church. But logically this meant rethinking not just the periods when the Church had suffered at the state's hands but also the times when the Church had benefited from an all-too-close relationship with it. What did it really mean to maintain a proper distinction between the temporal and spiritual realms? And when the Church had drawn upon coercive force had it honoured that distinction? Leo began to think it had not, famously telling French Catholics intent on overthrowing the secular Third Republic (and crowning a new Christian Bourbon king through whom the church could rule once more) that their cause was lost and their thinking outdated.

It was left for others to draw the deepest implications of this paradigm shift. From Leo's conviction about the freedom of the Church flowed a conviction about the freedom of the believer. The Sorbonne-educated Parisian intellectual Jacques Maritain, the most influential lay Catholic thinker of the 20th century, worked through this logic in Man and the State (1951). He also drafted Article 18 of the Universal Declaration of Human Rights in 1948: "everyone has the right to freedom of thought, conscience and religion", including freedom to change your religion and freedom to practise it "in community with others".

Most important of all is the Second Vatican Council's Declaration on Religious Liberty, Dignitatis Humanae (1965). This is the moment when the Church really demonstrated what it had learnt from its own experiences of, in the declaration's own words, "force [being] brought to bear in any way in order to destroy or repress religion . . . in a particular country or in a definite community". Religious liberty is no political expedient — the Church has learnt that religious freedom must be rooted in the dignity of the human being. People are truth-seekers — therein lies their dignity — and the only authentic way of seeking truth is in the context of free inquiry.

But religious freedom must also have real content to it; it can't be too abstract. The declaration thus fleshes out what the right to the free exercise of religion must entail: on the one hand, immunity from being coerced into belief; on the other, immunity from being restrained from practising faith.

Next, the Church has had to learn that religious freedom will always be threatened if it is construed too narrowly. It must mean more than the right to pray silently to the God of your choosing in the privacy of your own room. It has to include what Combes despised: ministering in public, being allowed to be outward-facing, and to share freely what you believe to be true about the world.

Finally, the declaration shows the Church to have at last learnt the deepest lesson of all: "The right of all citizens and religious communities to religious freedom must be recognised and respected." The prophet Lamennais has finally been vindicated: religious liberty must be a reciprocal right.