40 Yet since in the course of these same years, certain doubts have arisen concerning either the correct meaning of some parts of Leo's Encyclical or conclusions to be deduced therefrom, which doubts in turn have even among Catholics given rise to controversies that are not always peaceful; and since, furthermore, new needs and changed conditions of our age have made necessary a more precise application of Leo's teaching or even certain additions thereto, We most gladly seize this fitting occasion, in accord with Our Apostolic Office through which We are debtors to all, to answer, so far as in Us lies, these doubts and these demands of the present day.
Source: Quadragesimo Anno (Vatican.va)