Truly, this grand assumption is nothing more than circular reasoning as Ransom Dunn points out:
The affirmation, that the greatest motive invariably governs, is a mere assumption, incapable of proof. We ask, how does any one know that he is governed by the greatest motive? The answer, and the only answer possible, is, that he is thus influenced. But, how does he know that he is thus influenced? Because the greatest motive governs. And thus the assumption is the proof, and the proof the assumption, and finally they are both assumptions, incapable of any proof. This is reasoning in a circle with a short curve. It is simply saying that we know how man is influenced, because we know the nature of the cause; and we know the nature of the cause, because we know how he is influenced.
These “assumptions” amount to little more than tautology, as I described in the combox of another post:
Also, the Calvinist (at least those who follow Edwards) begs the question with regards to choosing according to our greatest desires. Well, how does the Calvinist know this? How do they know we never make choices according to an inferior motive or desire? The answer: the choice always reflects the greatest desire, or else the choice would not be made, since we choose according to our greatest desire (which is circular and reveals a tautology, “the prevailing desire always prevails” or “the prevailing desire is the prevailing desire”, etc.- which isn’t saying much).
It reduces to a bare assertion. It is our greatest desire because we choose it, and we choose it because it is our greatest desire. Therefore, “choice” and “greatest desire/strongest motive” become conflated so that the claim is simply “we choose because we choose”, or “we choose according to our choice”. And yet Calvinists try to paint Arminians as illogical because they believe the Arminian position amounts to “we choose because we choose”. That is not an accurate description of the Arminian view, while it is essentially what the Calvinist, who lodges the objection, actually believes.
It is also interesting that many Calvinists complain that Arminians base their arguments for free will on intuition, while appealing to intuition concerning the belief that we always choose according to our greatest desire…
Therefore, if it comes down to a battle of competing intuitions, I think the libertarian free will position will always come out on top, since the belief in free will and the subsequent reality of accountability seems to be among the most basic and universal of all human intuitions. If the Edwardsian Calvinists want to claim that their position is superior because it does not rely on intuition, then they need to explain how they came to know that we always choose according to our strongest desire or motive force. But even that is not enough. They also need to explain what makes the strongest desire/motive force the strongest desire/motive force. Where does the particular motive get its irresistible weight from? Can they demonstrate that the agent himself does not freely assign the greater weight to any particular motive over another?