William Perkins (1558-1602), in his 1595 Exposition of the Apostles’ Creed, on the question of effectual call, wrote:
Againe, if the Vocation of every man be effectual, then faith must be common to all men either by nature, or by grace, or both: now to say the first, namely, that the power of believing is common to all by nature, is the heresie of the Pelagians, and to say it is common to all by grace, is false. All men have not faith, saith Paul. 2. Thess. 3. 2. nay many to whom the Gospel is preached, doe not so much as understand it and give assent unto it; Satan blinding their minds that the light of the glorious Gospel of Christ should not shine unto them, 2. Cor. 4. 4. And to say that faith is partly by nature and partly by grace, is the condemned heresie of the semi Pelagian: for we cannot so much as thinke a good thought of our selves, 2. Cor. 3. 5.
This understanding of the teaching of Pelagius, who denied that “in Adam’s fall sinned we all, i.e., he denied that either Adam or Christ were federal representatives, who denied the doctrine of original sin, who made sin a matter of imitation so that we become sinners when we sin, is the common property of the majority of the Western, Augustinian tradition.
Further, Perkins spoke for the entire Reformation when he distinguished between full-blown Pelagianism and “semi-Pelagianism” which admits the federal relationship and original sin but which tends to downplay the effects of sin. As Perkins observed, semi-Pelagianianism also affirmed the necessity of grace but just as it watered down the effects of sin so it weakened the necessity of and the power of grace. Like Pelagius, for the semi-Pelagians, which included some of Augustine’s opponents in the early 5th century and much of the medieval church, faith is “partly by nature and partly by grace.” The semi-Pelagian view is that grace helps but it is not decisive. The free exercise of the human will, or in some cases, the human intellect or affections is decisive and essential for faith, justification, and salvation. According to semi-Pelagianism, from a Pauline and Protestant point of view justification is no longer by grace alone, through faith (trusting) alone, but now through grace and works (our cooperation with grace).
There is, thus, a good lot of Pelagius in semi-Pelagianism. This is why the Synod of Dort condemned the Arminian (Remonstrant) doctrines of having brought “again out of hell the error of Pelagius.” (Rejection of Errors, 2.3). If one reads Pelagius’ commentary on Romans one sees that the Synod had a point. Pelagius and semi-Pelagius weren’t that far apart.
With that background in mind one can imagine how surprised I was to hear the claim that it is semi-Pelagian to teach that faith is the instrument of mystical or existential union with Christ is “semi-Pelagian.”