I have to say, considering that Adam and Eve were "as little children" in the Garden of Eden, they both have a grasp on the English language far above anything that I can aspire to. Book IX of PL is a prime example of the use of rhetoric and it illustrates the dangers of it's misuse as Satan crafts a solid-seeming argument for eating the fruit that induces Eve to eat. But this begs the question: how much of this did Eve already have in mind? I'm not suggesting that Eve set out that day with the intent to eat the fruit and openly defy God, but I do wonder how much she had progression in mind. Even in Milton's version of the paradisiacal Garden of Eden, the Garden seems to be a place of stasis—pleasant stasis, granted, but stasis nonetheless. The existence is apparently one of gentle garden work in lopping, pruning, propping, and binding the plants of the Garden each day. To what effect, though? The fruit grows freely and plentifully in the Garden and there is always plenty to eat, and Eve says that any work that they do is essentially undone in one or two nights (see ll. 209-212). So what is the point of their labor in the Garden? Perhaps God was giving them "busy work" until the Fall happened.
Milton gives us a sense that Eve is seeking to prove herself out of some misplaced pride, but I think there is an argument to be made for her seeking progression from her current state. After all, one of the most appealing arguments that the serpent makes to her is that by eating she will ascend to a higher plane of existence. He says, "...in the day / Ye eat thereof, your eyes that seem so clear, / Yet are but dim, shall perfectly be then / Opened and cleared, and ye shall be as gods, / Knowing both good and evil as they know" (ll. 705-709). Eve wants more than the simplicity that she and Adam experience in the Garden. She wants to achieve higher things and reach higher levels. Adam appears fairly content in this simple existence, but Eve wants more.
Latter-day Saints have a different view on the Fall of Adam and Eve, of course, and as a Mormon I'm obviously going to bring some of that to what I read. Probably Milton didn't give Eve as much credit as we do when it comes to her decision to eat the fruit, but I don't think she is meant to be seen as an idiot. After all, he basically has Eve quote himself in making her arguments. Milton said in the Areopagitica, "As therefore the state of man now is, what wisdom can there be to choose, what continence to forbear without the knowledge of evil?" (location 32231). Eve reflects this sentiment in Book IX when she says "And what is faith, love, virtue unassayed / Alone, without exterior help sustained?" (ll. 335-336). No progression is possible without knowledge.