[Lord of Angmar]

The term "psychological depth" seems to me to be simply the extent to which the reader can understand the thought processes of the characters and relate to the characters on an individual basis. Characterization is the process of building and explaining the persona or disposition of a character for the purpose of the story, in which case neither psychological depth nor characterization is a substratum of the other. Characterization seems to me to deal with advancement of the plot whereas creating psychological depth in writing is a means of making the reader care about the advancement of the plot. In this case, I would say (from my own rather biased perspective) that Tolkien succeeded in his efforts to create pyschological depth. Certainly he does not delve deep into the psyches of each individual character, but such is not to be expected (nor necessarily desired) in epic writing.

What he does do is provide the reader with an often subtle and often blatant advancement of the motivations and emotions of his characters. Take Aragorn for example. He is indeed left mostly uncharacterized throughout the whole of Book One, but nevertheless through his actions in defense of the hobbits and through his overall persona we are given an ambiguous look at his disposition, personality and psyche. His own inner turmoil is brought to light by Boromir's words at the Council of Elrond. When Boromir openly questions Aragorn's ability to wield Narsil reforged, we see Aragorn's lack of assuredness at his own preparedness to do so, giving us the groundwork for the plight that Aragorn faces. In "The Ring Goes South" in the Fellowship of the Ring, there is a particularly moving although subtle hint at the doubt and anxiety that Aragorn will face on his pending journey:

Aragorn sat with his head bowed to his knees; only Elrond knew fully what this hour meant to him.

Given the furthering of his characterization in Rivendell (the revelation that he is in fact the heir of Isildur and that he will journey with the Fellowship at least until Minas Tirith) gives psychological depth to the above quote. Throughout the rest of his journey, the amazing burden that rests on his shoulders is made clearer. When Gandalf falls, he must lead the Fellowship, and it is clear he is entirely uncertain in his mind what to do after Lothlorien. It is also clear that the decision is tormenting him, and the fact that he puts off the decision to the last possible moment (where it is basically made for him by the coming of the Uruk-hai and the flight of Sam and Frodo) adds psychological depth to his character in that it illustrates his reluctance to make large decisions and his anxiety when faced with such decisions.

After Helm's Deep, when he reveals himself to Sauron via the Palantir and decides on his own to venture the Paths of the Dead to reach Gondor, his character grows in depth, as once again it is illustrated how deeply he is burdened with the task of getting to Gondor and, ultimately, defeating Sauron. This scene also advances the psychological depth of Aragorn in that it shows him growing as a person, being able to face a number of choices and willfully make a decision.

In the final stage of his physical and psychological journey, he is at first uncertain, coming to Minas Tirith but fighting on its flanks instead of claiming command over it. However, he becomes quickly decisive after the Battle of the Pelennor Fields, understanding the many variables of the War and coming to the conclusion that he should march with a host to Mordor, there to divert Sauron's attention away from Frodo and Sam and give the two hobbits a final chance in their quest of utmost importance. By now the reader is emotionally attached to the journey of Aragorn (at least I was, and still am upon re-reading the books). When he becomes King, the reader feels a connection with him, and a sense of fulfillment and pride in the fulfillment of his quest.

Of course, this is just my take on this character, and of course many of you may not agree with my definitions of psychological depth and characterization. I believe that the two coincide and depend upon each other, and in the case of Aragorn and many of the other characters, I felt that through characterization, through advancement of the plot and through subtle or obvious hints about the mind states and thought processes, there was a real sense of psychological depth achieved in the characters of Professor Tolkien's works.

Cheers,
Angmar