Non possumus, meaning "we cannot", is a Latin religious phrase originating from the story of the martyrs of Abitina, when emperor Diocletian prohibited Christians, under pain of death, to possess the Scriptures, to meet on Sunday to celebrate the Eucharist and to build premises for their assemblies.
It is not meant to express powerlessness, but, on the contrary, a strong moral determination.
Another ecclesiastic usage of the term has been attributed to pope Leo the Great, who wrote in 448 "quibus viventibus non communicavimus mortuis communicare non possumus' (i.e., we cannot hold communion in death with those who in life were not in communion with us)." This principle has been used to justify various Church policies, from refusal to hold funeral liturgies, to the lifting of excommunications on deceased individuals, and to objections to ecumenism and general relations with the non-Christian world.
In the 19th and 20th centuries, Non possumus was the name given to the diplomatic policy of popes Pius IX, Leo XIII, Pius X, Benedict XV, Pius XI and Pius XII in their relations with foreign powers, especially after the capture of Rome, where the pontiff became the prisoner in the Vatican and deliberately chose to limit his contacts with the outside world. It is generally thought that the Second Vatican Council downplayed this earlier Church policy.
This Latin phrase is also connected with the modern history of Poland. On 8 May 1953 Polish bishops sent a formal letter to the party leaders of the communist People's Republic of Poland declaring their decisive "no" to the subordination of the Church to the communist state. In retaliation, the government jailed the Cardinal Stefan Wyszyński.