Regarding the soundtrack for S4, I've noticed a new motif that originated in TST, a sombre violin piece that begins at 1:13 on track 6 'Running Away', used for the scene where John reads the letter Mary wrote about running away. So naturally I assumed this was Mary's theme, until today when I heard it again in TLD (track 7 of the TLD soundtrack 'No Charges' at 0:45), but slowed down. The scene in TLD is where John hits Sherlock, so it has nothing to do with Mary. What may we deduce of this?
Here’s “Running Away”:
And here’s “No Charges”
What struck me first of all, on Running Away, WAS THE GODDAMNED VIOLIN. A lot of us speculate that Mary’s letter is ACTUALLY Sherlock’s letter that he wanted to write to John when he left him at TRF. Alright, stay with me here for a second: Sherlock writes his “love songs” on violin, and they’re always melancholy and ALWAYS for John (sorry, but Irene’s Theme is FOR JOHN); I think this is ACTUALLY meant to represent Sherlock’s character and his pining for John, his apology for leaving him. It’s also tightly intermingled with hints of John’s theme sped up in it as well.
Then, in No Charges, you are correct – it’s DOES bear a terribly striking resemblance to Running Away, just played an octave or semi-octave down or on a different scale. Which causes it to sound SADDER. Because now Sherlock feels like he is getting what he deserves for leaving John, doomed to a life of infinite sadness and loneliness. Technically, it’s also relating to Mary since they are discussing Mary in that scene, but yes, I do honestly believe anything played by the violin in ANY of the soundtracks are a reflection of Sherlock’s feelings.
God I actually cried writing this. I hadn’t had the chance yet to listen to S4′s soundtrack, so I’m glad I got to for this.
If you’re interested, there’s interesting meta about the entirety of the S4 music here by @holmesianscholar!