encyclical

for an encyclical to be infallible the Pope must speak ex cathedra.

要使不谬，教皇必须发言有权威性。

Popes seldom weigh in on economic matters and rarely in the form of an encyclical, one of the most authoritative forms of papal writing.

教皇们很少会讨经济问题，也很少以形式颁布。是教皇文件中最具权威性一种。