Papal Infallibility was made a Dogma by Pope Pius IX at the First Vatican Council In 1870. Shortly thereafter, Saint John Henry Newman wrote a defense of the new Dogma, known as “Letter to the Duke of Norfolk”, carefully laying out the many conditions which must be met before any Papal (or Conciliar) Declaration can be considered infallible. This talk is a discussion of those conditions, drawn from on the Saint’s letter. The text is found as Chapter 11 of the letter, and is available at https://www.ecatholic2000.com/newman/duke-11.shtml .