Board Thread:Theories and Speculation/@comment-27002073-20160406173133/@comment-734582-20160408081244

I wanted to add that the sharingan does not truly copy abilities. Kakashi simply used Genjutsu to make it look like it did.

Rather, it gives insight into an enemy's techniques, allowing the user to rapidly learn how it's done, and do it themselves. Copying is an emergent power, so to speak. Since it allows the user to see chakra, well it's a lot easier to know what you're doing if you can see what you're doing.