Can the suffering souls in purgatory help people on earth by their prayers?
There are two opinions on this question. The first is founded on St. Thomas Aquinas, who explains why it is that we do not generally pray to the souls in purgatory, as we do to the saints in heaven. Those who are in purgatory though they are above us on account of their impeccability, yet they are below us as to the pains that they suffer: and in this respect they are not in a condition to pray, but rather in a condition that requires us to pray for them. (ST, II-II, Q. 83, Art.11, ad 3) The real problem presented by St. Thomas Aquinas is that the poor souls in purgatory have no way of knowing of our prayers, that they might be able to answer them. They cannot know them as the blessed in heaven, who see all our needs and prayers in the vision of God, nor can we personally ask for their prayers, as we can of the living on earth: Those who are in this world or in purgatory do not yet enjoy the vision of the Word, so as to be able to know what we think or say. Wherefore we do not seek the