im very much new, i've been reading some music theory books for general and specific to guitars.

Now what i do not understand is the following

  • how a Chord is constructed?
  • how does a formula became to be in constructing a chord? like, in triads, why i do i use specifically 1-3-5 notes in a major scale? in 7th, why do i only use 4 notes (1-3-5-7). Yes, there are variants in using 1-3-5 and 1-3-5-7, each with its own sharps and flats. However, what i do not understand is why do i need to only use specifically those notes (1-3-5 | 1-3-5-7) in a scale? why not use all 7 or why do i not use 1-2-5?

Thanks for any inputs. again im still a newbie

5 Answers 5


One of the fundamental ways of thinking about chords involves "stacking thirds". From a scale perspective this means taking every other note in the scale. To build a CMaj7 chord, start with a C Major scale, or more specifically, start with the C Ionian mode, and take every other note: C-E-G-B. You can continue into the next octave to get the chord extensions (9th, 11th, and 13th): C-E-G-B-D-F-A. That chord is a CMaj13.

You can build a G7 chord in the same way, but starting from the 5th degree of the C Major scale, i.e. the G Mixolydian mode. G-B-D-F. To get the chord extensions, continue into the next octave: G-B-D-F-A-C-E. That is a G13, and contains the 9th, 11th, and 13th. Note that a chord symbol with a 9, 11, or 13 implicitly contains the lower extensions.

Yet, those implicit extensions may be left out in practice. For example, it is especially common on guitar to see 13th chords spelled with only the root, 3rd, 7th, and 13th. A G13 spelled this way is G-B-F-E, and a common shape for this is:


In jazz we often play chord fragments instead of full chords. This has a lot of implications; it allows more space for soloists when you are comping, it allows more freedom when you are playing solo and chord melody pieces, it can provide nice ambiguities when multiple chords may be implied, and sometimes it can provide a nice texture. To do this, it is often best to think of chords as the notes that you want to include rather than a big collection of notes from a scale. You might need a C9 chord; you could play C-E-Bb-D-G:


This is a common shape for C9 that includes all of the notes, but the 5th is not too important to the sound of the chord. The 3rd establishes whether the chord is major or minor, the 7th establishes whether the chord is a major or dominant 7th chord, and the 9th is an extension. In some ways the 9th is the most important note in a 9th chord, so in some cases you might just play the root and the 9th, or add the 7th if you want, or the 3rd and the 7th. If you want a more open sound on a C9 you could try:


This chord contains only the root, 7th, and 9th of a C9. With no 3rd, it is ambiguous: it could be a C9, or it could be a Cm9. Here is a very ambiguous chord that I sometimes use in place of a C7(b9):


This isn't even really a chord by itself, containing only the root (doubled) and the b9. But it is an effective sound to use at times.

Summing up, learn the basics of how chords are constructed, i.e. by stacking 3rds (know that you can also stack 4ths or 5ths for other chord types). Learn which notes are important in chords, and build the chords that you need. There is a correct way to spell a C7(b9) chord in theory (C-E-G-Bb-Db), and while there are incorrect ways, there is no one correct way to spell C7(b9) in practice.

  • What are those chord descriptions? I’ve never seen them before.
    – Erik
    Feb 14, 2019 at 10:08
  • Nevermind, they just came out different on my phone
    – Erik
    Feb 14, 2019 at 12:35

In tonal music (major/minor key music) the chords are called tertian meaning built of thirds.

As you already know the triad is two thirds, the seventh chord is 3 thirds.

...why not use all 7?

You can. 1 3 5 7 9 11 13 that would be a thirteenth chord. How common thirteenth chord are will depend on style. Not common for something like Haydn versus more common in modern jazz.

...why do i not use 1-2-5?

You could have such a combination of notes, like C D G. But, as the chord system is tertian - again, meaning based on thirds - we would give special consideration to that group of tones. It doesn't match a group of notes by thirds and typically it may be labelled a suspension where the C is 'suspended' until it moves down to B thus creating the group B D G which is tertian chord. So the suspension is not regarded as the proper chord. The group of tones the suspension resolves into is considered the proper chord.

The is a such thing as quartal harmony where chords are built of fourths. In that system 1-2-5 is a proper chord. Actual quartal harmony is found in modern composition styles and in some jazz.

When identifying chords you do need to know whether the harmonic style is tertian or quartal.


I think you can find details "how a Chord is constructed" in other questions in this website, but it seems like you already know the basics. So your main question seems to be "why are chords constructed the way they are".

This is a fair and maybe profound question. I can't give you a lot of details, but the reason is merely historical. Western harmony is based on thirds. So you stack some thirds and then you have chords! Of course there are also physical reasons why these notes sound nice together, but you don't see 7th chords in traditional arabian or japanese music, do you? Their music evolved in a different way.

Of course you can use 1-2-5, or all seven notes, or whatever you want! Feel free to construct chords without being stuck to formulas. Chances are, you will find that the chords that sound "right" and more familiar are third based chords, because that's what we've been used to hear all our lives, that's how western music has evolved over time.

To open your mind a little bit, you can take a look for example at Set Theory. I have already composed something based on set theory, and you can't even imagine the cool stuff that can come up when you are not stuck to traditional functional harmony!

So, if you are looking for details on chord construction, take a look at the other answers. If you are looking for the reasons why chords are stacks of thirds, look into western music history. If you are looking for alternative ways to construct chords, set theory may be a starting point, but there is a lot more stuff out there!


Well the simplest answer is you're not forced to build chords by stacking thirds. You are free to do anything. Music theory is only a description of existing (western in this case) practice of music making. And you basically study that practice following recipes like: build chords by stacking thirds.

That being said, chords built this way make the most of existing western music from classical to pop to jazz. And even if we play 1-2-7 we might 'hear' it as reduced form of dominant chord as we tend to aurally refer to established forms, harmonies etc.

So it's a bit like - you take first karate lessons and ask: why do I need to kick this way and not another? The old and wise karate master will probably respond: well you can do it your way, but it will work much better if you spend next 10 years figuring out why we all kick this way and why it works.


When constructing a chord, you want the notes to sound nice along with one another. Mathematically, if you look at those notes, 1-3-5, they fit along what’s called an overtone series. Take an A chord for example. Your base note, A, had a pitch of around 440 Hz (depending on your preference). The notes C# and E are produced as overtones. If you want, you can read more up on that, but it gets very complicated very fast.

There are 4 types of triads, and 4 types of 7th chords. For triads, you have Major, Minor, Diminished, and augmented. Naturally, the overtones play along the major scale, so when you make the 3rd minor (in a minor chord), it doesn’t sound pretty, at first. Because they play along another overtone series, much much more desecrate than the base Major chord, the resulting notes can be interpreted as an alternate “feeling” such as sad. The same goes for diminished and augmented chords.

Basically, you are playing notes that work well with others, in an order that they will sound well. For example, if you play a 7th chord such as Cmaj7, the notes you would play are C,E,G, and B. If you play B and C right next to each other, it sounds terrible. That is because the frequencies are so close to one another, they just don’t work well. But when you put space in between them, they work with the overtones, and that beautiful sound of a Major 7th chord is created.

This might have been the most confusing thing you have ever read because I don’t think I explained it correctly, so if you have any questions don’t hesitate to ask!

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