Can I borrow a chord?

Can I borrow a chord or two? You sure can!

Think of all those 1980s hair-band boys with long hair, makeup, and frilly clothing. They basically dressed up like girls and somehow made it look cool. And remember the hard-rock girls who cut their hair short and acted tough -- you sure wouldn't pick a fight with them, but you still loved to look at them.

Yes, rock culture has no qualms about borrowing stuff from the opposite sex and making it work out. And rock music is just as free about borrowing chords from the opposite mode. If you're in C major, you can throw in chords from C minor (the parallel minor). And if you're writing in C minor, the chords from C major (the parallel major) are fair game.

These chords borrowed from the parallel major or minor are called borrowed chords.

In a minor key, using the major [five] or [five]⁷ chord provides decisive cadences that you can't quite get with [five]m. The major [four] in might help a minor-key song sound a little more bright and open.

In a major key, the minor [four]m chord strikes a poignant note, while the minor [five]m might help create an introspective atmosphere.

You can jump back and forth between major and minor flavors of a chord. This sequence is a favorite of ELO's, using both flavors of four:
[one] [four] [four]m [one]
In the key of C, that's C | F | Fm | C

Guiffria's "Call to the Heart" uses major [five] in the verse and switches to minor [five]m in the chorus to anchor the song's distinctive, memorable hook. (Here's Call to the Heart on YouTube.)

When a tornado picked up Dorothy in Kansas and put her back down in the parallel land of Oz, she said to her little dog, "Well, Toto, I don't think we're limited to just three chords anymore." That trip opened up so many harmonic possibilities for Dorothy, it was almost like switching from black-and-white to technicolor.