Co-redeemer is an interesting issue. It is a dogma of the Catholic Faith that Jesus Christ alone is our Redeemer.

ex cathedra[/i]]...God, through His Son, Jesus Christ our Lord, who alone is our Redeemer...

This being said, the titles of co-Redemptrix and co-Redemptress do not seem to be intrinsically heretical in and of themselves, but depend upon the explanation given for their usage.

Consider the prefix "co" which comes from Latin:

"co", pref.

   1. Together; joint; jointly; mutually: coeducation.
   2.
         1. Partner or associate in an activity: coauthor; cofounder.
         2. Subordinate or assistant: copilot.
   3. To the same extent or degree: coextensive.
   4. Complement of an angle: cotangent.


As can be seen from the definition of "co", we can indeed hold that Mary was a partner or associate in the redemption, albeit with a completely different role from that of Jesus Christ. Without Christ's sacrifice, there would be no redemption, as He alone is our redeemer, and Mary, as co-Redemptress played a subordinate and different role in His work.

Pope Leo XIII used the title of co-redemptress in regards to Mary:

For in the Rosary all the part that Mary took as our co-Redemptress comes to us, as it were, set forth, and in such wise as though the facts were even then taking place; and this with much profit to our piety, whether in the contemplation of the succeeding sacred mysteries, or in the prayers which we speak and repeat with the lips.

The "co-" prefix in co-Redemptress/co-Redemptrix can only refer to Mary's cooperation; it does not mean that Mary is co-Redeemer, that she redeemed anyone, not even with and under Christ. (The "co-" prefix should not be capitalized, since it refers to our mere human efforts towards our salvation - Mary's participation; the "R" in co-Redemptrix should be capitalized since it refers to Divine efforts towards our salvation.) Mary was subordinate (co) to Christ's work (Redemptrix).

Pope Leo XIII made no move to say that Mary herself did any redeeming.

Antipope Benedict XV, on the other hand overstepped his bounds and spoke material heresy, taking this concept further than what was lawful:

As she suffered and almost died together with her suffering and dying Son, so she surrendered her mother's rights over her Son for the salvation of the human race. And to satisfy the justice of God she sacrificed her Son, as well as she could, so that it may justly be said that she together with Christ has redeemed the human race.

This would imply changing the title co-Redemptress, used by Pope Leo XIII, into co-Redeemer, which change is heretical.

The Blessed Virgin Mary, as worthy of honour and veneration as she is, above all creation, did NOT redeem the human race at all. She participated in the redemption by providing the human flesh, which nature Christ took from her, but she did not redeem the human race with Him. Anything that she merits for us, or that we merit through her intercession, can only be merited because Jesus Christ's perfect sacrifice was of infinite value, without which valuable sacrifice we and Mary could merit nothing.

Being so closely united to Christ in His sufferings, however, it is fitting, though not owed to her, that Mary should be elevated in glory beyond any human being other than Christ Himself, but to say that Mary is our redeemer, that she redeems anyone, in any way is heretical, even if it is with and subordinated to Christ, since this renders the decree from Trent false, which says that Christ alone is our Redeemer.

It is not heretical to say, as Pope Pius X did, that she merits (de congruo, or something freely given out of God's gratuitous mercy) grace and salvation for us, nor is it heretical to say that she was co-Redemptrix, provided we do not believe this means she performed the same task as Christ (merit de condigno, or something merited by strict justice), but that she was subordinate to God in His task, while playing an altogether different role.

Therefore it may not justly be said that Mary together with Christ has redeemed the human race, because according to justice, only God could make such a purchase (you cannot demand a purchase unless it is OWED to you in strict justice), with the fitting price of His human blood and the intrinsic and infinite merit of the Divinity of the same, nor are we all "co-Redeemers".

What the hell do you think "co-redeemer" means if not "redeemed with" you stinking idiot?  Your arbitrary malicious will presents itself again, for you exonerate Leo XIII but condemn another using the same language.  Why don't you just assert that Leo ACTUALLY meant "Co-Equal Redeemer" like you impute to Benedict?  And if the term "Co-Remprtrix" is already defined, why do you arbitrarily imput your own definition when reading someone else's words?  Ah, it's because you are a blithering, moronic idiot who doesn't possess an ounce of virtue, that's why.  And why do you keep bringing up the same basic doctrine of the sole mediatorship of Christ as if that is really an issue since no one, especially Benedict, denies it.  You've already admitted that the language doesn't negate the sole mediatorship of Christ.  The only explanation is that you are a blithering, moronic idiot who doesn't possess an ounce of virtue.  You are in fact just another breed of protestant.