In order to tackle the problem of ecclesiastical heresy, late medieval theologians elaborated on the idea of fraternal correction. Alexander of Hales laid the foundation of the standard theological discourse, which was developed by Thomas Aquinas. In applying this concept to the problem of papal heresy, William of Ockham questioned and reversed the hierarchical assumptions and premises in the traditional discourse. Drawing on his ethical theory of invincible ignorance, he also provided a moral basis for an inferior's dissent from ecclesiastical authority. Ockham's emphasis on the inalienable obligation of conscience in defence of ecclesiastical disobedience shows a striking similarity to some of John Locke's ideas on religious toleration.