To which Saints may a Catholic pray, and when can this begin? The Catholic Church teaches, as I understand it, that a person may pray to a Saint, and this Saint will then intercede along with that person to God concerning the request (or something like that).  It appears that Mary may be the saint to whom people pray the most.

My question concerns which saints are qualified to receive prayers.  Is it restricted to only those who are designated as Saints by the Catholic Church?  Does that start only after the Saint is designated as such?  What is people prayed to John Paul II or Mother Theresa today, but they receive the designation of Saints at a later time?  Is it the designation of sainthood by the current Pope on earth that allows someone in heaven to begin hearing prayers?

What prevents any Christian from hearing the prayers of people on earth?  Would it have something to do with the time when they get out of Purgatory?

I understand there are several questions there, but they all surround the issue of praying to the Saints.
To which Saints may a Catholic pray, and when can this begin?

Actually a catholic can privately pray to anyone whom he/she thinks can intercede on their behalf. In fact Catholics do not see any difference in asking you to pray for me and asking my dead grandma (if I believe she is in heaven or purgatory) to pray for me.

Is it restricted to only those who are designated as Saints by the Catholic Church?

Public prayers are restricted only to canonized personssee note 1. But private prayers/veneration is not. In-fact the actual canonization procedure can start if and only if for 5 years after the death of a person, the lay faithful have prayed to them privately and continuously. But such prayers can not be done publicly in a Church or Chapel. More specifically their statues and pictures cannot be placed in an alter of a church/chapel. They cannot be represented with halo around their head.

Is it the designation of sainthood by the current Pope on earth that allows someone in heaven to begin hearing prayers?

No it does not. The designation of sainthood or canonization only attests that the universal church can pray to them because this person is in heaven and has the power to intercede before God for us. The main purpose of Canonization is to show people Good example. This is revealed by infallible papal proclamation. Canonization is helpful only for people on this earth to recognize a saint, it does not give special powers to people in heaven. Private devotions are not restricted by this.

What prevents any Christian from hearing the prayers of people on earth? Would it have something to do with the time when they get out of Purgatory?

On the contrary, a catholic can even ask for the holy souls in the purgatory to intercede. Only thing is that souls in the purgatory cannot pray for themselves, but they can very well pray for us.

Points to note:


Persons who are beatified can be publicly venerated only in the concerned persons diocese. For public veneration outside of his own diocese the permission of the Bishop or the Bishop council of the country is required. Such restrictions do not apply for one who is canonized. For example Bl. Mother Theresa is permitted to be venerated all thru India by the Catholic Bishops council of India, even though she belongs to the Archdiocese of Calcutta.
There are some saints whose devotion is explicitly suppressed because faithful have been having devotion to them, but their life is not a good example or there is little to no proof for their existence. For example as late as 1173 Pope Alexander III, reprimanded certain bishops for having permitted veneration of a man who was far from being a saint. Also the names of St. Valentine and St. Philomina are removed from universal church canon, because of lack of evidence for them to have existed. But their veneration is permitted in local churches where it is traditionally held.