The Canons of Dort, First Head of Doctrine, Rejection of Errors, Paragraph Eight
Synod condemns the error of those ...
VIII Who teach that it was not on the basis of his just will alone that God decided to leave anyone in the fall of Adam and in the common state of sin and condemnation or to pass anyone by in the imparting of grace necessary for faith and conversion.
For these words stand fast: He has mercy on whom he wishes, and he hardens whom he wishes (Rom. 9:18). And also: To you it has been given to know the secrets of the kingdom of heaven, but to them it has not been given (Matt. 13:11). Likewise: I give glory to you, Father, Lord of heaven and earth, that you have hidden these things from the wise and understanding, and have revealed them to little children; yes, Father, because that was your pleasure (Matt. 11:25_26).
Dr. Kim Riddlebarger, pastor of Christ Reformed Church in Anaheim, CA, and co-host of the White Horse Inn, provides an excellent explanation of this portion of the Canons of Dort. Here's how it begins . . .
The error identified and refuted in paragraph eight is one which attempts to locate reprobation in people’s misuse of their freedom, not in the sovereign will of God. According to this error, people somehow manage to reprobate themselves, by using their free will in such a way as to disqualify themselves from that which they could have otherwise obtained–salvation from sin. In other words, these people could have co-operated with God’s grace, and then believed the gospel. Instead, they “chose poorly,” as someone once put it.
This erroneous notion results from the Arminian contention that despite the fall of the human race into sin, men and women are still able to co-operate with the grace of God, and when they do so, they are thereby inclined to believe, repent, and live in holiness before God. When the logic of the Arminian view is applied to those whom do not chose co-operate with God’s grace (the reprobate), the reason given as to why these people are not numbered among the elect is because they did not chose to believe, repent, and live a holy life before God. To put it crudely, they reprobated themselves by not co-operating with grace.
You can read the entire explanation here.