Understanding triads - the basic chords of music

What are triads?

Triads (in their simplest state) are chord types composed of three notes separated in pitch by intervals of major 3rds and/or minor 3rds. They are the most basic complete chords in music and every music student or musician of pitched instruments should be familiar with them, especially those who study or play a harmonic instrument, such as piano or guitar.

If you play the notes C, E & G at the same time, you're playing a triad. It has three notes and the spacing or interval between the notes C & E (CDE) spans three letters as does the interval between the notes E & G (EFG). That's what makes them thirds.

So both of those intervals (C to E and E to G) are thirds because each spans three letters, but if you know about semitones in music, you'll see that they aren't equal in size.

(A semitone, also called half step in the US is the interval between any note and the next nearest in pitch up or down, e.g., adjacent frets on a guitar, or black to neighbouring white keys on a piano.)

C and E are separated by 4 semitones, (C to Db to D to Eb to-E) while E and G are separated by just three semitones (E to F to Gb to G). To distinguish between both types of third, the larger (4 semitone) one (C to E) is called a major 3rd and the smaller (3 semitone) one (E to G) is called a minor 3rd.

So the notes CEG form a triad composed of a major 3rd plus minor 3rd. Triads with that arrangement are called MAJOR TRIADS (or simply, major chords) and this particular one is the chord C MAJOR.

Types of triad

As we saw, major triads consist of a major 3rd plus a minor 3rd. There are, in fact, only four possible ways of arranging two major and/or minor 3rds. Each arrangement produces a different type of triad, so there are only four triad types. They are as follows:

Intervals
Triad type
Examples based on C
,major 3rd + minor 3rd
MAJOR
C major (C E G)
minor 3rd + major 3rd
MINOR
C minor (C Eb G)
major 3rd + major 3rd
AUGMENTED
C augmented (C E G#)
minor 3rd + minor 3rd
DIMINISHED
C diminished (C Eb Gb)

Triad arrangements

As mentioned at the start, the above explanation describes triads in their simplest form. However, they are still triads if they contain any of the following features:

The intervals of thirds that separate the notes don't have to be simple major or minor thirds. They can be compound major or minor thirds. Using again our example of C, E & G, the interval from C to the next E above is a simple major 3rd, but C to the E that lies one or more octaves above the nearest E is a compound major 3rd. The actual pitch register of the notes doesn't matter. It's still a triad.

Any of the notes can be duplicated at any octave any number of times, So while the basic C major triad consists of C, E & G, there can be any number of Cs, Es and Gs. Think of a large orchestra ending a symphony on a C major triad. All of the instruments will be playing either C, E or G notes - from the deep notes of the double bass all the way up to the high notes of flutes and piccolos. Dozens of Cs, Es & Gs covering a huge pitch range and all played at the same time - the chord is still a triad.

The notes of a triad can be arranged in any order. CEG, CGE, EGC, ECG, GCE, & GEC are all different voicings of the same C major triad.

If any note other than C, E or G is included, the chord will no longer be C major, but some other chord type. And with more than three differently named notes, it will no longer be a triad.

The C major scale showing the C major triad as scale notes 1, 3 & 5
The C major scale showing the C major triad as scale notes 1, 3 & 5 | Source
The intervals separating the notes of a C major triad
The intervals separating the notes of a C major triad | Source

Root, 3rd and 5th

Another way to look at triads is in terms of the notes compared to a scale. The scale of C major, for example, is CDEFGABC. Our previous C major triad example, consisting of notes C, E & G can be seen in the scale as the first, third and fifth notes.

So, the notes of a triad can be named as the 1st (or root), the 3rd and the 5th (regardless of any octave doublings).

When comparing other triads we can still refer to the major scale but the notes are numbered as follows:

  • Major = 1 3 5
  • Minor = 1 b3 (flat 3) 5
  • Augmented = 1 3 #5 (sharp 5)
  • Diminished = 1 b3 b5

Inverted triads

Although a triad can have any number of doublings, and although the notes can be in any order, the choice of the lowest (bass) note has a significant effect on the sound, so these are named as follows:

If the lowest note is the root, the chord is said to be in root position. For example, C major arranged as C E G (or C G E) in order of ascending pitch is a root position C major triad.

If the lowest note is the 3rd of the chord, the triad is said to be in first inversion. C major arranged as E C G or (E G C) is a first inversion C major triad

If the lowest note is the 5th of the chord, the chord is said to be in second inversion. C major arranged as G C E (or G E C) is a second inversion C major triad.

Note that when a triad is inverted, certain intervals will no longer be 3rds if we count from the bass. It's still a triad, though, because the required 3rds are counted from the root with the notes arranged in scale order.

For example, the second inversion C major triad has notes G, C & E, which produces intervals of a 4th and a 6th above the bass note, G. Despite having no 3rds, it's still a triad because when re-arranged in scale order from the root, the notes will be C, E & G and the 3rds will be back in place.

Recognising triads by ear

Listen to and compare the sound of root position triads based on the root note C.

Triads in standard notation

Triads in notation
Triads in notation

Various arrangements of the four triad types based on C

some of the countless possible arrangements of the 4 triad types based on C
some of the countless possible arrangements of the 4 triad types based on C

Beyond triads

Extensions
Triads are the basic chord units of Western 'tertian' harmony (harmony based on 3rds). As you saw, they're composed of stacked major and/or minor 3rds. Even more major or minor 3rds can be stacked on top of those to produce chords that aren't triads but are extensions of triads. Stacking more 3rds produces 7th, 9th, 11th and 13th chords.

Non-triads
All triads, regardless of the number of doublings in any particular arrangement, will have only three different note names that (when arranged in scale order) will be separated by major and/or minor 3rds (simple or compound ). If either of those conditions aren't met, it's not a triad. For example, suspended 4th chords have only three differently named notes (e.g., Csus4 = C F G) but they're not triads because the intervals between the notes aren't 3rds and can't be re-arranged as 3rds. Some modern classical theorists have expanded the definition to include intervals other than major and minor 3rds, but in mainstream traditional classical theory, they're not recognised as triads.

Incomplete triads
Incomplete major and minor triads are often found in music. The 5th may be left out. It's the least active of the notes and its absence is barely noticed. It's the 3rd of the chord that gives it its distinctive major or minor character. Power chords (5th chords) on the other hand have just the root and 5th and mustn't have a 3rd (or they'll no longer be power chords). The key and chord progression, however, often imply the missing 3rd as either major or minor - so power chords often function as triads, even though they're not.

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