According to Catholicism or Eastern Orthodoxy are there any doctrinal barriers to Christians sharing places of worship with non-Christians? Hagia Sophia was originally the seat of the Patriarch of Constantinople, then the chief mosque of the Ottoman Empire, then a museum. A few days ago, it reverted to being a mosque once more. Numerous Christian religious leaders have decried this last transition (as, in my opinion, they ought to), but it left me wondering what a long-term resolution of the matter would actually look like.
The building could, in principle, revert to being a church. Personally, I feel that, given the centuries of history that Muslims have with said structure, this would be unjust; and, in any case, short of a Christian reconquest of Constantinople/Istanbul, it's never going to happen. Atatürk's compromise of turning the building into a museum seems well-intentioned but ultimately unsatisfactory: this building was built for the glory of God.
The one remaining option that I can see is to share the building. Christianity's and Islam's holy days seldom overlap. Could the building be a church on Sundays and a mosque on Fridays? I'm a practising Roman Catholic myself, and I can't think of any insurmountable reason forbidding sharing a place of worship outright. There are, after all, stories of Catholic priests celebrating the eucharist in Auschwitz; I can't imagine that any putative unholiness brought on by reciting the Quran could compete with an extermination camp. But I'm far from an expert, and I hardly need to add that the Eastern Orthodox perspective would be essential in the case of Hagia Sophia.
And, of course, Hagia Sophia is just a prominent example. There are plenty of other locations, e.g. the Mosque–Cathedral of Córdoba, where it might be reasonable for Christians to share a place of worship with another faith.
According to current Catholic Canon Law, sharing a space in the manner proposed would pose problems.
Canon 1205: &quot;Sacred places are those which are designated for divine worship or for the burial of the faithful by a dedication or a blessing which the liturgical books prescribe for this purpose.&quot;
Canon 1210: Only those things which serve the exercise or promotion of worship, piety, or religion are permitted in a sacred place; anything not consonant with the holiness of the place is forbidden. In an individual case, however, the ordinary can permit other uses which are not contrary to the holiness of the place.
While it might be justifiable for a non-Catholic Christian group to use a Catholic space in accord with their customs as long as in the church &quot;cleanliness and beauty are preserved as befit a house of God and that whatever is inappropriate to the holiness of the place is excluded.&quot; Canon 1220, that would be much harder to support for a religion entirely distinct and theologically at odds with Catholicism.
The comparison to Auschwitz is unsuitable. One case is making due with the best which is possible given the circumstances (i.e. the alternative would be not having Mass at all) and the other would be an ongoing situation. Canon Law, like civil/common law has a general, but not absolute law principle along the lines of necessity not obligating strictly (or you are not bound to the impossible).