It's a mysterious thing. Why do songs sound happy or sad depending on whether they're in a major or minor key? Mathematically the two are barely distinguishable. A song in C major uses the same notes as one in A minor, they're just arranged differently.
So why the difference in emotional response? There's some evidence that this is learned, not innate. A lot of Eastern European folk music, for example, is in a minor key, but it's supposed be upbeat and celebratory. Your reaction may vary according to the culture you were raised in. Plus, a lot of it is to do with tempo and instrumentation. 'Livin' On A Prayer' is in E minor, but only a maniac would describe that song as a work of keening melancholy.
This has been on my mind today thanks to the following videos, the first of which has suddenly gone viral. All of them are minor-key songs, digitally shifted to major. It's strange how such a subtle change can completely alter the tone of a song, utterly robbing it of its power.
Sounds like Mumford And Sons.
Sounds like Mr Big.
Sounds like the Mike Flowers Pops.
Of course, this trick works the other way as well. You can give any tune, no matter how jaunty, an atmosphere of tension and dread with only the slightest of tweaks. Proof? The Super Mario Bros theme in a minor key sounds like this.