Modernism is the heresy of heresies, because it carries within it all previous heresies, being as it is a direct, frontal assault upon faith and all doctrine and dogma. It is liberal theological opinions developed in the late 19th and early 20th centuries. The term came to prominence in Pope Pius X 's 1907 encyclical Pascendi dominici gregis, which synthesizes and condemns modernism as embracing every heresy.