The first is that Edwards' redefinition of "contingency" sets him against his Reformed heritage. According to Muller, the old notion of contingency had to do with the possibility of the contrary. Edwards, on the other hand, sees contingency as being something without a cause.
Since Edwards argues that contingency is impossible (again, according to his "new" definition of contingency), and that all who affirm contingency are grouped together with the arminians. Well, since the older standardbearers of Reformed Orthodoxy affirmed contingency (albeit by a different definition), then Muller reasons Edwards to be opposing the old Reformed Orthodoxy.
The problem, which should be obvious, is that Edwards is not directly opposing the old Reformed standardbearers. He is opposing a different view of contingency - one in which acts of the will can occur without any direct causal connections. If anything, Edwards is talking past those who went before him. Edwards' obvious developments do not represent a true sea change so much as a contemporization. It is not an opposition, but rather, an improvement.
Over at Wes White's blog, he had mentioned in a brief exchange, Muller's citation of WCF 9.1 as a potential ground for seeing Edwards as unorthdox. Permit me to quote that section of the Confession, for clarity's sake:
9:1 God hath endued the will of man with that natural liberty, that it is neither forced, nor by any absolute necessity of nature determined to good or evil.At first glance, this may appear to be a painful blow to Edwards. But consider that if we understand this section to be denying the necessary connection of the will and the nature (as a condemnation of Edwards via WCF 9.1 would require), one must shoot themselves in the foot, because then in WCF 9.3, the absolutely necessary connection of the nature and the will are affirmed, though not in as many words. Observe:
9.3: Man, by his fall into a state of sin, hath wholly lost all ability of will to any spiritual good accompanying salvation: so as, a natural man, being altogether averse from that good, and dead in sin, is not able, by his own strength, to convert himself, or to prepare himself thereunto.Even if the language of absolute necessity is absent, it should be obvious that the understanding of 9.1 which condemns Edwards (lets call this understanding "Schema One") cannot then make sense of 9.3.
Let me suggest an understanding of 9.1 which also comports with 9.3 and Edwards (we'll call this "Schema Two").
"God hath endued the will of man with that natural liberty, that is neither forced..." Lets stop here for a moment. By bringing in the language of "force," the Confession is referring to an external coersion. It is not rejecting an internal coercion, because that would make hay of 9.3. The language of "force" here is a reference to external influences which necessarily move the will. in other words, we are not robots.
"...nor by any absolute necessity of nature determined to good or evil." This is a denial of a strictly physicalist understanding of human nature. Hobbes was a physical determinist, but Edwards was not. This portion of 9.1 is a denial of the sort of determinism one might find in Hobbes, for example. (By the way, I believe that the interpretation presented by Schema Two is affirmed by A.A. Hodge in his commentary on the Confession (pg. 219-220).
Again, if you deny Schema Two's understanding of this last quoted portion, you are left in a badly compromised situation of trying to explain how one's nature can be wholly unable, per 9.3, to will any spiritual good while denying that one's nature can be necessarily determined one way or another.
Look at Turretin on the idea of physical determinism:
Predetermination does not destroy but conserves the liberty of the will. By it, God does not compel rational creatures or make them act by a physical or brute necessity. Rather he only effects this – that they act both consistently with themselves and in accordance with their own nature, i.e., from preference and spontaneously (to wit, they are so determined by God that they also determine themselves). (Turretin, Page 569-570)It is this sort of determinism ("a physical or brute necessity," as Turretin calls it) which WCF 9.1 opposes, according to Schema Two. I wish to strongly suggest that it is not the sort of compatiblistic, Edwardsian necessitarianism which WCF 9.1 is opposing.
In fact, if WCF 9.1 were opposing the sort of necessity being suggested by Edwards, we would find ourselves in quite a strange spot. On the one hand, the claim is made by Muller that nobody was using this sort of language to explain the activity of the will, prior to Edwards. Yet on the other hand, it is suggested by Edwards' opponents in this matter that it is precisely Edwards' sort of view of the will which is being condemned by 9.1. So we essentially have a non-existent model of the will being rejected in WCF 9.1, if, in fact, the proponents of Schema One are correct. It would be most unusual for the Westminster Divines to feel compelled (no pun intended) to include a renunciation of a non-existent understanding of the will, a hundred years before it sprang into existence.