Dicit ei Pilatus: quid est veritas?

"In the judgment of Fr. Rosa – and of Pius X – modernism was "a new form of Christianity that threatened to overwhelm the ancient one." To oppose it, it had to be struck at its philosophical root, the error from which sprung all the other errors in theology, morality, culture, and practical life. The fundamental error attributed to the modernists was that of denying the capacity of reason to know the truth, thereby reducing everything – including religion, and including Christianity – to subjective experience." (source)

Read Pascendi Dominici Gregis for yourself (English) at the Vatican website.