I just finish reading The Silver Chair in the Chronicles of Narnia series and I never understood why the book was called The Silver Chair If you know why please let me know.
Remember the prince's thrown was silver chair, I think the witch used it to subdue him. The children broke it
If there isn't literally a silver chair...my guess would be that it's a symbol for being seated in a high place. Something like: being handed the world on a silver platter, maybe. I'd probably have to read it, to tell you. That's just my guess.
The Silver Chair was the chair that served as a prison when Prince Rilian was sane and in his right mind. It was also the manifestation of the Lady's spell. Without the Silver Chair, there would be no spell and there would be no conflict.
The prince sat in the Silver Chair nightly and it was only at that time when he became his real self. All other times he was under the influence of the spell. See page 143, (chapter 11 In the Dark Castle) the paragraph beginning, Quick, I am sane now...If only I could get out of this enchanted chair... It poses quite the dilemma for the other characters, but having read it, you already know that.