Can the souls in Purgatory pray for us?

The common teaching, though not solemnly defined, is that the holy souls can and do pray for the living, especially for those who have aided them. St Thomas Aquinas held the contrary: the souls are not in a state to pray, but are rather to be prayed for (Summa Theologiae II-II, q. 83, a. 11, ad 3). St. Robert Bellarmine, the great Doctor of the Church, defended this position (De Purgatorio, Book II, ch. 15). The practice of invoking the "holy souls in Purgatory" is widespread in Catholic piety and has never been condemned by the Church. St. Alphonsus Liguori encouraged the faithful to invoke the holy souls as powerful intercessors (The Great Means of Salvation, Part I, ch. 1). The Catechism teaches that 'our prayer for them is capable not only of helping them, but also of making their intercession for us effective' (CCC 958).