Modulations are central to the art of tonal music. This article can get you started.

Whether you're a songwriter, a classical musician, or an electronic musician, studying the chorales of Bach will develop your harmonic creativity towards mastery.

Build beautiful chord progressions, and then sing them.

After intervals, chords are the next-level building block of musical organization. This article shows how I think about chords and their progressions, and teaches you fundamentals for composing with them.