“It should be understood, however, that Reformed theology does not, like Arminian theology, regard the doctrine of common grace as a part of Soteriology. At the same time it does recognize a close connection between the operations of the Holy Spirit in the sphere of creation and in that of redemption, and therefore feels that they should not be entirely dissociated” (Louis Berkhof, Systematic Theology).
According to Berkhof the facinorous figment of “common grace” in the sphere of creation is not a “part of Soteriology” (sphere of redemption), though he does say “that they should not be entirely dissociated.”
In some areas of Reformed theology there is diversity and disagreement rather than absolute uniformity of thought and exposition on the fiction of “common grace” (e.g., per the Berkhof quote above: how close the connection; to what degree associated or dissociated?).
Here is a quote from Reformed theologian W.G.T. Shedd explaining the differences, nuances, and gradations between various damnably heretical views of “grace” that are NOT truly grace (Romans 11:6). From the single volume edition of Shedd’s Dogmatic Theology:
“If common grace should prevail over the sinner’s resistance, it would be saving grace. This is not the same as saying that the sinner by a right use of common grace makes it saving grace. In this latter case, there is a cooperation of the sinner with God in regeneration. The sinner by working concurrently with common grace renders it effectual. This is synergistic regeneration and involves conditional election. But if without any right concurrent working of the sinner’s will common grace should overcome the sinner’s resistance and do the whole work, the regeneration would be due to God alone. To overcome the sinful will is not the same as to assist it ” (See supplement 3.6.24.) (W.G.T. Shedd, Dogmatic Theology, p. 348; underlining mine–CD).
 WS: Cf. Edwards, On Decrees and Election 59-62; Howe, Reconciliableness of God’s Prescience with His Sincerity; Baxter, Directions for Spiritual Peace and Comfort 1.252 (ed. Bacon).
I agree that Shedd presents a distinction WITH a difference. I agree that to “overcome the sinful will is not the same as to assist it.” The difference is that Shedd’s “common grace” is more powerful than the “common grace” of his brothers in Satan. To adapt Habakkuk 1:16 to Shedd’s distinction between a synergistic and monergistic dragnet.
“Therefore they sacrifice unto their net, and burn incense unto their drag; because by them their portion [is] fat, and their meat plenteous” (Habakkuk 1:16).
One execrable idol operates synergistically and the other monergistically (and that makes it all better).
The following is a footnoted supplement from Shedd that expounds a bit on what he wrote above. Shedd makes an overt and brazen attempt to force “common grace” into Luke 10:13 with an Eiffel Tower-sized shoehorn.
“3.6.24. (see p. 348). Christ (Luke 10:13) declares that if the common grace to Chorazin and Bethsaida, which was ineffectual with them, had been granted to Tyre and Sidon, it would have been effectual with these. The miracles (dynameis) together with the ordinary influences of the Holy Spirit which produced no repentance in the former case, he says, would have produced it in the latter. According to this statement of our Lord, the very same amount of divine influence may succeed in overcoming a sinner’s opposition in one instance and not in another. When it succeeds, it is effectual and irresistible grace; when it fails, it is ineffectual and resistible. This shows that grace is to be measured relatively by the result and not absolutely by a stiff rule which states arithmetically the amount of power exerted. All grace that fails, be it greater or less, is common; all that succeeds, be it greater or less, is special. In order to have effected repentance in the people of Chorazin, it would have been necessary to exert a higher degree of grace than was exerted upon them; while in order to effect repentance in the people of Tyre, no higher degree would have been requisite than that exerted upon Chorazin. But it is to be carefully noticed that the failure in the instance of Chorazin was owing wholly to the sinful resistance made to the grace; and the success affirmed in the instance of Tyre would be owing not to any assistance of the grace by the cooperation of the sinful will of Tyre, but wholly to the overcoming of Tyre’s resistance by the grace exerted. The sinful will of the inhabitants of Tyre, in the supposed case, was a wholly resisting will like that of the inhabitants of Chorazin and hence could not synergize with the divine Spirit any more than theirs could, but the degree of resistance, according to our Lord’s statement, was less” (W.G.T. Shedd, Dogmatic Theology, p. 365).