"A shadow & a thought"

[Firefoot]

Son of Númenor got here before I did, and I agree with everything that he said. Only a few things of my own to add.

Éowyn loved in Aragorn what she saw in him - not what he was but how she perceived him. She saw him as a high and valiant lord, willing to die for his cause (and a valiant death in battle, I imagine Éowyn thought it would be), which he was, at least part of him, but that was all Éowyn saw him as. She did not see his 'true colors' so to speak. She didn't see the part of him that wasn't a king but the man you see in "Flotsam and Jetsam":

He wrapped his grey cloak around him, hiding his mail-shirt, and stretched out his long legs. Then he lay back and sent from his lips a thin stream of smoke.
"Look!" said Pippin. "Strider the Ranger has come back!"
"He has never been away," said Aragorn. "I am Strider and Dúnadan too, and I belong both to Gondor and the North."

So Éowyn sees her ideal of him in Aragorn, hence the "shadow". I never felt that shadow was used in a negative sense, but rather it was like a shadow of Aragorn - like him and part of him but not him.

One other place that I can think of where shadows are not used in a negative way:

From the ashes a fire shall be woken,
a light from the shadows shall spring.

Again referring to Aragorn, except here he is the 'light'. But the shadows here aren't referring to evil. I always thought of it like the back corner where nobody ever looks, like in an attic. Virtually no one (in Gondor, etc...) ever thought that a king would come again out of the North - the shadows. So I think that Tolkien is using the word "shadows" in a couple different ways. One for evil, one for forgotten times and places, and a third for an ideal or perception.