This is a Blaugust 2026 blog post. I’m now in my third term of music theory. Back in the first term, I created a handy reference sheet for major and minor scales. I just added a new ref sheet for what’s called applied (or secondary) chords. A Bit of Music Theory (If you know basic music theory, go ahead and skip this part.) First, listen to this music snippet: Here is the music score for what you just heard: If you enumerate the C major scale – C-D-E-F-G-A-B – you see that C is the first note. The chord built on top of it is a C major chord, and is denoted by roman numeral I. Similarly, F is the fourth note on the scale. The chord built on it is an F major chord, and is denoted by roman numeral IV. And the final chord in the sequence is the V chord, a G major chord. This sequence is the I-IV-V chords in the major scale. You’ve heard this a zillion times. So, what comes next in the song? Probably a C major chord. Your ear really, really wants to hear this resolve back to a C major chord. Listen again and tell me if that’s not true! In music theory, we say that the V chord in a major scale is a dominant chord, because it wants to resolve back to the I, called the tonic chord. Now, let’s make one teeny change to the song: we’ll add one chord to the sequence. Listen to this: Here is the music score for that snippet: Whoa! Remember how in the first snippet the G major chord wanted to resolve to the C major chord really badly? But here, in this second snippet, the song wouldn’t mind hanging out for a bit on that same G major chord. And who knows where it will go after that? That added chord is a D chord, and it’s called a secondary dominant chord. It greatly changes the character of the G major chord that follows. It makes it a temporary tonic – a stable, resting place – in the song. You get a secondary dominant chord by building a chord on the 5th degree above the target. In this case, the target is G major. So the secondary dominant of G major is: G-A-B-C-D … the D major chord. Applied Chords Ref Sheet That’s just one example of how secondary dominant chords can be used. Secondary dominant chords are part of a class of chords called applied chords (or secondary chords) that let you “tonicize” any chord in the key. There are a number of options, across major and minor musical scales. I created a reference sheet to help identify and construct these chords. Here it is: You can download a copy from here: pub.crosenthal.com/music-theory-refs/applied_chords.pdf The project that generates my music theory reference sheets is open source. The code is posted here: codeberg.org/crosenthal/music-theory-refs If music theory is your thing, I’d love to hear your feedback. Enjoy!