I had asked AC a question on the free will thread, and I wanted to pursue it a little without derailing that thread. Here is a portion of what AC posted in response to my question:

Originally Posted by AC.
Hi Newman,

I hope these quotes explain where I'm coming from....

The modern Roman Catholic church clearly embraces a heretical form of Semi-Pelagianism which affirms that man has a need for God's grace (for man is too weak to help himself), but man by his own free will is able to decide whether he wants God's grace. Whereas Pelagius taught that salvation is totally man's own doing, and Augustine taught that salvation is totally from God, Semi-Pelagianism teaches that salvation is a combination of the efforts of both man and God. According to RCC Semi-Pelagianism, salvation is accomplished when man decides to co-operate with God and accepts the grace God offers him. and also must maintain his own just standing before God by merit and good works. This is often viewed as a synergistic concept of salvation. Whereas Reformed Protestants also affirm the necessity of good works, yet they are the inevitable result of salvation, not the cause of it.

What I wanted to pursue further was whether or not the above definitions of Semi-Pelagianism are accurate. It was my understanding that the label "semi-pelagian" was used to describe the idea that while the grace of God is necessary to turn man toward God (a rejection of Pelagius) it was no longer necessary after that (a rejection of Augustine) and hence the term "semi." The Lutheran Formula of Concord (1580) says this:

Quote
We reject also the error of the Semi-Pelagians, who teach that man by his own powers can make a beginning of his conversion, but without the grace of the Holy Ghost cannot complete it. Epitome of the Formula of Concord: Free Will: 10 http://www.bookofconcord.org/fc-ep.php
Now, to me, the Concord definition seems to be a bit different from the definitions that AC posted, and it also seems to line up with the definition that I was familiar with and espoused. So, which one is correct? I was under the impression that the belief that man cooperates with the grace of God is not necessarily a heresy. Paul even uses the greek word "synergeo" in 2 Corinthians 6:1. I certainly agree that if one believes that grace is not necessary to persevere, that would be heretical. But I previously had not thought that cooperating with the grace of God so that the reception of His grace would not be in vain was heretical. Do you guys think I was wrong?