Éowyn and Merry both love Théoden deeply. Éowyn is under his authority as both his subject and his ward. Merry has sworn allegiance to him. Both of them blatantly disobey his direct orders, and this disobedience ends up having positive results instead of negative. What's happening here? Are we supposed to see Éowyn and Merry as bad examples or good ones? (A side note that Éomer was just as disobedient when he pursued the orcs even though commanded not to; that doesn't seem to get the same amount of attention from readers.)
Some people take the position that this is a case of God "writing straight with crooked lines" and bringing good out of the situation even though Théoden's two loyal subjects are doing a decidedly bad thing. But I think there's something deeper going on here that fits Tolkien's Catholic way of looking at things. Gandalf, who's the closest there is in Middle-earth to a direct emissary from Ilúvatar, doesn't scold Éowyn and Merry or lecture them or say anything negative about their actions to anyone. In fact, he seems to suggest they were exactly where they were supposed to be.
It surprises a lot of people, including not a few Catholics, to learn that according to Catholic theology, the highest authority is the individual conscience. This doesn't mean simply doing whatever we want; it assumes the person honestly desires to follow God's will and uses every aid available to discern what that is, including prayer, reflection, and outside guidance, as well as serious consideration of the Church's teachings (very serious consideration if the discernment involves going against one of them).
As a member of the "anyone but Ratzinger" camp during the 2005 papal election, I wasn't thrilled when we ended up with Pope Benedict; he always seemed to me to be more of a theologian than a pastor, more "ivory tower" than in touch with common people. As we experienced, this can lead to communication problems when you're talking to a broader audience than other theologians (like, say, the world), which could have made him seem more absolutist than he was. There's an example, I think, in a paragraph about him in a Time magazine commentary noting that in one address during his papacy, "The bulk of his message was directed at the West, at its disavowal of religious authority and its embrace of what Benedict called 'the subjective "conscience"."' (You know we're in trouble when we get a sentence with three layers of quotation marks!) The next sentence of the paragraph reads, "For Benedict, if your conscience tells you something that differs from his teaching, it is a false conscience, a sign not of personal integrity but of sin." That might be true; I wasn't inside Benedict's head, so I can't really say. But it's not a conclusion that can be drawn from his opposition to "the subjective 'conscience'." The subjective conscience is one that doesn't use the aids available to discern God's will, but looks at only its own (subjective) perspective. Western civilization's "disavowal of religious authority" doesn't mean sometimes disagreeing with what the Catholic Church says; it means not giving any consideration in the decision-making process to what's spiritually or morally right .
The root problem of the subjective conscience isn't that the person following it might end up disagreeing with Pope Benedict; it's that the person following it is already acting out of a false pride that says he or she has all the insight there is to be had on the subject, something none of us can claim. St. Augustine's "Love and do what you will" is a stricter law than any the Church would be able to come up with: it's a pretty tall order to be so rooted in love that we can completely trust our own will to lead us in the right direction; most of us need all the help we can get.
But, ultimately, if a person's honest best effort to discern God's will means disobeying legitimate authority, whether that be civil, familial, or religious, the person has a duty to be disobedient. Catholics have a great tradition of saints who were locked up in their own homes because they were determined to follow God's will rather than that of their parents. I think Éowyn and St. Clare would have understood each other quite well. Clare's great advantage was in having the guidance and support of not only individuals within the Church but of Church teaching itself. We might say Éowyn was forced to use "the subjective 'conscience'" because that's all she had available to her, a situation none of us has to face - thank God.
It's true that Éowyn's discernment process is anything but perfect. She really doesn't have anywhere to go for outside guidance, and she wouldn't have asked for direction from a God she believes is too distant to hear - or care. There's a self-destructive bent to her thinking that affects her judgment, at least partially related to her upbringing in a culture that sets a high value on dying well. But each of us has our own set of limitations and blind spots, and that doesn't excuse us from having to make decisions (or no one could ever decide anything). So, like Éowyn, we do the best we can. I know some people disagree with this, and think that Éowyn was completely irresponsible and wrong-headed, but I'll side with Gandalf (and, I'd say, Tolkien) on this one and believe that she was exactly where her best judgment - imperfect as it was - would have had her. Shouldn't she have been taking care of her people's needs? According to one definition of duty, yes, in the same way that Frodo should have stayed at Bag End so the Gaffer's taters wouldn't have been dug up*. Sometimes there really is a higher duty than the one that's assigned to us by authority. Imperfect as we are, we're constantly asked to assess that, in ways large and small.
In "The Passing of the Grey Company" Aragorn and Éowyn have a conversation about duty. What I find most interesting is that they're using the word in different ways. Aragorn doesn't understand this, and Éomer wouldn't have if he'd been present; this lack of understanding makes it necessary for Gandalf to take the two men to task in "The Houses of Healing."
In one way, at least, Aragorn has it easier than a lot of the major characters in LotR; he's known for many years what his duty in life is, and his own conscience has no debate with it. In fact, in Appendix A we find that his immediate reaction upon learning his royal identity is to go off into the woods and sing joyfully (and fall in love). Aragorn as a reluctant king exists only in the movies; in the book, he's champing at the bit, as we learn when he reminds Gandalf of how patiently he's been waiting and preparing. He may have a tough job, but at least he knows what his job is and doesn't have to buck legitimate authority, or even his own desires, in order to do it. Even his time of "doing his duty" by waiting and preparing was mitigated by the hope that it would be temporary; Éowyn sees no end to hers.
Like most of us tend to, Aragorn assumes that Éowyn's position is similar to his and that the word "duty" has the same connotations for her as it does for him. But, for Éowyn, it's much more complicated. The "duty" she's referring to when she uses the word disdainfully is something Aragorn hasn't experienced: being required to do something that interferes with what she believes is her true duty. In her mind, she lacks the freedom John Paul II refers to in the quote on this page: "...the right to do what we ought."
Even Merry's situation is less problematic than Éowyn's, because having grown up in the Shire he's used to making up his own mind about things. He seems to stay behind because of his physical limitations rather than a desire to be obedient. His "I won't be left, I won't," doesn't have any subservience in it. When Dernhelm offers him a lift, he doesn't fret about not following orders. If Merry and Éowyn had been older, they might have been more prudent. But their youth is part of who they are, and as Gandalf also reminds us in "The Last Debate," prudence is not always the best counsel.
It's interesting that on another occasion Aragorn encourages Éomer to look past his duty of taking any wanderers in Rohan to the king. He says, 'I do not think your law was made for such a chance,' implying that there are times the law shouldn't be followed. Éomer has to trust that the Three Hunters will come of their own accord to Meduseld, as Faramir has to decide to break the law to allow Frodo and Sam to continue on their journey. Faramir understands the consequences if he judges wrongly - his life will be forfeit - but he has the duty to do what he discerns is right.
*In the exchange between Frodo and the Gaffer in "The Scouring of the Shire," the Gaffer is absolutely correct, according to the social contract between landed gentry and their tenants. His difficulties are Frodo's fault because Frodo failed in his duty to look out for the needs of his tenants and/or servants. And Frodo acknowledges this, in the spirit of accepting the consequences of his decisions.