Thomas More Answers Slate's Question: Post-Mortem Prayer - Can praying for a dead person help get him into heaven?

In Dialouge Concerning Heresies, Thomas More answered the question posed at Slate:

Do Christians think praying can help a dead person get into heaven?

The answer, written by More in 1528:

You may for the most part both pray for them and pray to them, as you may for and to those who are still alive.  But someone who is canonized, you may pray to him to pray for you, but you may not pray for him...St. Augustine says anyone who prays for a martyr is insulting the martyr.  With regard to everyone, you can hope rightly and be seldom sure, but of the canonized you can consider yourself sure.