B. B. Warfield described the infiltration of Pelagian error in partial form this way:
But, as we have been told that the price of liberty is eternal vigilance, so the Church soon found that religion itself can be retained only at the cost of perpetual struggle. Pelagianism died hard; or rather it did not die at all, but only retired more or less out of sight and bided its time; meanwhile vexing the Church with modified forms of itself, modified just enough to escape the letter of the Church's condemnation. Into the place of Pelagianism there stepped at once Semi-pelagianism; and when the controversy with Semi-pelagianism had been fought and won, into the place of Semi-pelagianism there stepped that semi-semi-pelagianism which the Council of Orange betrayed the Church into, the genius of an Aquinas systematized for her, and the Council of Trent finally fastened with rivets of iron upon that portion of the Church which obeyed it. The necessity of grace had been acknowledged as the result of the Pelagian controversy: its preveniency, as the result of the Semi-pelagian controversy: but its certain efficacy, its "irresistibility" men call it, was by the fatal compromise of Orange denied, and thus the conquering march of Augustinianism was checked and the pure confession of salvation by grace alone made forever impossible within that section of the Church whose proud boast is that it is semper eadem. It was no longer legally possible, indeed, within the limits of the Church to ascribe to man, with the Pelagian, the whole of salvation; nor even, with the Semi-pelagian, the initiation of salvation. But neither was it any longer legally possible to ascribe salvation so entirely to the grace of God that it could complete itself without the aid of the discredited human will—its aid only as empowered and moved by prevenient grace indeed, but not effectually moved, so that it could not hold back and defeat the operations of saving grace.
The Plan of Salvation, Autosoterism, pp. 41-42
In a previous post, I provided a broad and reasonable definition of Semi-pelagianism from someone who cannot be considered an historical slouch. Nevertheless, in fairness to those who would prefer to define things a bit differently, I provide this alternative explanation. Under this explanation, obviously, the error described in this earlier post as "semi-Pelagian" would be described by Warfield as semi-semi-Pelagian. However, as I mentioned in that post, the point was not the label.
To summarize, in the set of definitions by Warfield:
1. The sufficiency of grace;
2. The necessity of initial grace; and
3. The general necessity of grace.
1. The sufficiency of grace; and
2. The necessity of initial grace.
1. The sufficiency of grace.
We (the Reformed) view each of these positions as deficient. By affirming sola gratia, we affirm the general necessity of grace, the necessity of initial grace, and the sufficiency of grace.
P.S. For more on the broader definition of Synergism generally as a species of Semi-Pelagianism broadly defined, see here: (link).