This is the best presentation of the difference between the Catholic and Calvinist positions I have ever heard.

Great lecture

Cooperating Grace is a misnomer because it is God who operates our conversion: God 'cooperates' WITH HIMSELF in the ensuing sanctification process. This is the source of modern-day semi-pelagianism because it makes MAN the principal agent of his sanctification - not God. Saint Augustine would have said that it is the Holy Spriti who 'rectifies' our will and, when our will is made to coincide with the will of God, God can act 'through' us without any resistance. Here is how saint Paul expresses the same idea: 'Being confident (..) that He who has begun good works in you will perfect them unto the day of Christ' - Philippians 1:6. It is MAN who 'cooperates' with God by renouncing evil and embracing the Good of his own Free will - not the other way around. It is God who converts us and then works through us - our only 'participation' is to allow Him to do so. To think that the imperfect will of Man can be the source of his sanctification is delusional: Man can do SOME good but will never do all the good Providence requires of him - only God is Perfect, which is why only HE can be the source of our sanctification.