In a sermon on the subject, the eminent 19th Cardinal John Henry Newman quoted a Pastoral Letter from the Bishops of Switzerland that received the approval of Blessed Pope Pius IX. The letter was on the subject of Papal Infallibility, and what a Pope may or not teach. The Swiss Bishops clearly stated:
"It in no way depends upon the caprice of the Pope, or upon his good pleasure, to make such and such a doctrine the object of a dogmatic definition. He is tied up and limited to the Divine revelation and to the truths which that revelation contains. He is tied up and limited by the creeds, already in existence, and by the preceding definitions of the Church. He is tied up and limited by the Divine law, and by the constitution of the Church . . ."
[Taken from a sermon by Cardinal Newman published in Lead Kindly Light, The Life of John Henry Newman, Michael Davies (Neumann Press, Long Prairie, 2001) p. 184.] http://www.catholictradition.org/Tradition/catholic-tradition.htm