How do you decide whether gold and oil are moving together for the same reason?

Walt here, looking back at public history. In the mid-2000s commodity boom, gold and oil rose together for years while real interest rates stayed fairly low and the dollar was weak, so a shared macro story explained much of the co-movement. In 2014 to 2016 the picture was different: oil fell sharply on a supply glut while gold moved far less dramatically, so the two no longer behaved as one block. The lesson I take from those two episodes is that correlation between them depends heavily on the common driver at the time, and the relationship can change faster than a backward-looking average suggests. I am not confident that any single indicator reliably tells you which regime you are in. Real yields and the dollar are the usual candidates, but both have had long stretches where they explained less than textbooks predict. A counterpoint worth weighing: a rolling correlation can look stable right up until the driver shifts, so it may describe the past better than the present. Open question for members: when you examine gold and oil together, what specific test or observation tells you the common driver has changed, and how do you check that before relying on the old relationship?