# The rule that Chord I, IV, and V are majors - does that extend to 7th chords?

So for example, in the key of G# major.

D# is the V chord

In major key the V chord should be a major, so does that mean if I am doing a seventh chord, it should be D#maj ? This would be: D#, G, A#, D. But āDā is not a note in the key of G# major.

So does the whole concept of Chord I, IV, V being major chords in a major key only extend to triad chords? does the seventh note not ascribe to the rules of being a major or minor (according to 1 4 5/ 7 /2 3 6), and rather the seventh note is whichever note fits into the key (so in this case it would be D#, G, A#, C#, a D#7 chord)?

• Whereby the triad of D# is: D#, F##, A# – Albrecht Hügli May 1 '20 at 11:23

Interesting question. Firstly, let's consider only using the notes that are diatonic - those actually from the major scale and key. Don't know why you chose G♯ - it's a more complicated scale than its enharmonic of A♭, and with loads of sharps, will complicate the issue.

So, I'll keep it simple in key C. Notes are CDEFGAB. Making 'seventh' chords involves starting with a basic triad, and adding the next note one third above the highest. So, C maj. =CEG. Adding a B note makes it CEGB. C major seventh. Playing the IV uses FACE - another M7 - F major seventh. The V chord, GBD has F added, making G dominant seventh. Those three are the mainstay used in a lot of pieces - they keep happily within the key (which is NOT a rule!!) The next most used will be C7, comprising CEGB♭, which sort of belongs to another key - F. And often it's used in key C in order to get to the chord F.

I wish you hadn't used G♯ as the key. True, there's no D note, only because we don't use two different notes with the same letter name in scales. This question could have been answered using that key, but I can't be responsible for the suicide rate of any subsequent readers! So please, forget that key!!

The base problem is that there are many different types of seventh chords. There's major seventh, with major triad and a M7 note on top. There's dominant seventh, with a major triad and m7 on top. There's minor seventh, with a minor triad and m7 on top. There's diminished seventh, with a minor third, diminished fifth and a dim 7 note on top. There's also more, but it's already gone past what you asked about.

• Hi, thank you so much for this detailed explanation! To be honest I'm only just starting to learn music theory, I chose G# at random! I didn't realise it was such a complex issue but I should have guessed considering its music theory... – Amelia May 1 '20 at 14:56
• You could do a lot worse than reading some of the questions (and answers) on this site. And when there's something you don't understand, pose another question. Just avoid key G#! – Tim May 1 '20 at 15:00
• Music theory isn't as complicated as it's made out to be. For this sort of question, you might do well to start by memorizing the Circle of Fifths: it's literally a circle with 12 positions (like a clock) that represent the 12 (15) most common keys (it is technically 15, but 3 of them are aurally equivalent to each other: Db/C#, Gb/F#, Cb/B). C is at the top, and moving to the right a position moves you up a perfect fifth (G), moving left a position moves you down a perfect fifth (F), and so on. Most music theory gets easy when thought about relative to the Circle of Fifths. – John Doe May 1 '20 at 21:51

I7= major 3rd, perfect 5th, major 7th

IV7= major 3rd, perfect 5th, major 7th

V7= major 3rd, perfect 5th, minor 7th

this is not a rule, this is the law derived of the diatonic scale and this doesn't change whether we are in C or in Eb, or in C# or in D#

P.S.:

As the tetrad of D (Dmaj7) is D, F#, A, C# - if D = I or IV - so the tetrad of D# (D#maj7) is D#, Fx A#, Cx. (x = ## -> double sharp!)

Or when D7 = V7 (D, F#, A, C) -> D#7 = D#, Fx, A#, C#)

As Tim says it is not quite obvious why you choose D# major and not Gx major! (so the dominant V7 of CX would be Gx, Bx, Dx, Fx (theoretically you can add as many sharps as you want without confusing beginners - just ignore the sharps when reading!)

Btw: The last section was just joking ;)

• When I see '7' after a letter or Roman numeral, I think 'dominant seventh'. So writing I7 along with V7 could be confusing, since one is shown as major seventh, the other as dominant seventh. – Tim May 2 '20 at 6:25
• How would you then write the C maj7 in RN? and what is IV7 if not F maj7 – Albrecht Hügli May 2 '20 at 17:23
• I use that little triangle for maj 7. With a letter or a Roman numeral. – Tim May 2 '20 at 17:30
• Yes, now I remember: in a blues I use to read I7 and IV7 as minor seventh. – Albrecht Hügli May 2 '20 at 17:36

You appear to be cataloguing the chords that can be made from the notes of a scale - the diatonic chords in a certain key.

It's not a 'rule', just a list of what chords can be built from the notes C. D, E, F, G, A, B (if we're in C major) or G♯, A♯, B♯, C♯, D♯, E♯, Fx (if you insist on taking G♯ major as an example!)

Yes, if you restrict your choice to diatonic notes, the 7th chord built on I will be a major triad with a major 7th. The one built on II will be a minor triad with a minor 7th. etc.

We could list some 9th, 11th and 13th chords as well. The 13th chord on IV in C major would be F, A, C, E, G, B, D. (But remember, we DON'T call that F13.)

But so what? It's just a list of the permutations and combinations of the notes in a scale. Definitely not a list of PERMITTED chords when a song's in a certain key.

When you ask about key and used symbols like `I`, `IV`, `V`, I assume you are asking about functional, common practice harmony (basically the style of Handel and Mozart.) Sometimes the harmonic system is called the major/minor system.

In major and minor keys the dominant chord is a major triad or a dominant seventh chord.

Other seventh chords are used. Probably the other two to get acquainted with are the `ii6/5` minor seventh in major (`iiĆø6/5` half diminished in minor) and the full diminished seventh chord built on the leading tone `viio7` in major or minor. Seventh chords are usually in the second half or advanced section of harmony textbooks. I suggest learning those common seventh chords first - by identifying them in real scores - before taking the deep textbook dive.

In `G#` major the dominant seventh chord would be: `D# Fx A# C#`. The `x` is a double sharp. Those accidental spellings are awkward, because the more typical thing is to call that key `Ab` major with a dominant of `Eb G Bb Db`.

Enharmonic equivalence digression: `G#` and `Ab` major are called enharmonically equivalent meaning the pitches are the same but the letters and sharps and flats differ. consider just the starting tones. `G#` and `Ab` are the same key on the piano (key meaning the keyboard key.) `G#` and `Ab` are enharmonically equal, but one or the other will be used depending on the harmonic context. In the case of key signatures, you usually go with the one that uses the fewest sharps and flats. `G#` major uses 6 sharps and one `F` double sharp. `Ab` major uses only four flats so `Ab` is the one used. You can call `G#` major a theoretical key signature meaning you can writing it, but it's very impractical!

If you are just getting started with studying theory and harmony, learn your key signatures. It will take some time, but in the end things will be a lot easier to understand when you know the keys and how to "spell" chords correctly.

Whether a chord is major or minor depends on its 3rd - so your plain V triad is major because it contains that major 3rd, right? You can stack another note on top to get a 7th chord, but it won't change that major tonality.

What might be confusing is that maj7 is referring to the fact you have a major 7th in there, not whether the chord itself is major (in fact you can have a minmaj7 chord!). So the V being a major chord doesn't require a major 7th, and as you've noticed, it usually has a minor 7th instead!

When you're building chords like this you're basically stacking thirds, and in practice that means you're starting on a scale degree, skipping a note and taking the next one. So all the notes in your chord are within the key, and for the V you get a major chord, and when you add another third to get a 7th chord, you end up with that minor 7th.

That's also what gives it its function, the major 3rd and minor 7th in there are a tritone apart, so there's dissonance that wants to pull back to the I chord and resolve (they both shift away from each other, so the 3rd and 7th of the V become the root and 3rd of the I respectively)

• The last paragraph sounds a little confusing! – Tim May 2 '20 at 6:29
• This is how I would have answered the question, but the last paragraph may be more advanced than a newbie might be able to understand without further study, however I'm all for promoting further study. – skinny peacock May 3 '20 at 17:27
• @skinnypeacock yeah that's why I added it at the end, kind of as a little taster for the more advanced stuff, but also because it's the reason you don't want a maj7 chord there - it needs that major 3rd and minor 7th to really do its thing. I hope it didn't make it too confusing because I was going for the simple answer! – cactustictacs May 3 '20 at 18:39