Music theory part 1 – Basic Intervals and chords

Recently I started to take on my old hobby of music making and playing the keyboard, so i had also the need to brush up my knowledge on music theory.
These series of posts are mostly a summary for myself of information I found all over the internet. This first post concerns about basic intervals and chords.

Intervals

An interval is basically the distance between 2 notes. These distances or intervals have names and are used as building blocks for chords.
Some of the most common intervals are listed in the table below:

NameDescriptionExamples
Half stepBasic interval.
White key -> Black key
Black key -> White key
(except between B and C and E and F, which are 2 white keys)
C - Db
B - C
Whole step2 half steps
White key -> White key
(except between B and C and E and F)
D - E
E - F#
Major 3rd2 whole stepsF - A
C - E
Minor 3rd1 whole step
1 half step
(or Major 3rd - 1 half step)
F - Ab
C - Eb
Perfect 5th3 whole steps
1 half step
(or Major 3rd + Minor 3rd)
C - G
Db - Ab
Diminished 5th3 whole steps
(or Perfect 5th - 1 half step)
E - Bb
D - Ab
Augmented 5th4 whole steps
(or Perfect 5th + 1 half step)
F# - D
C - Ab
Major 7th5 whole steps
1 half step
(or Octave - 1 half step)
C - B
Ab - G
Minor 7th5 whole steps
(or Major 7th - 1 half step
or Octave - 1 whole step)
C - Bb
F - Eb
Diminshed 7th4 whole steps
1 half step
(or Minor 7th - 1 half step
or Octave - 1 whole step and 1 half step)
C - A
E - Db
Octave6 whole steps
C - C'
F# - F#'

Chords

A chord consists of 3 or more notes separated by particular intervals.

Basic triads

A triad is a chord that consists of 3 notes. See the following table for the basic triads. The composition column indicates which intervals make up the chord from a particular root note. The notation column indicates how the chord is commonly written in non staff notation.

TypeCompositionNotationExample
MajorRoot -> Major 3rd -> Perfect 5thROOTNOTEC
C - E - G

Ab
Ab -> C -> Eb
MinorRoot -> Minor 3rd -> Perfect 5th(ROOTNOTE)mCm
C - Eb - G

F#m
F# - A -Db
DiminishedRoot -> Min 3rd -> Diminished 5th(ROOTNOTE)dimCdim
C - Eb - F#

Edim
E - G - Bb
AugmentedRoot -> Major 3rd -> Augmented 5th(ROOTNOTE)augCaug
C - E - Ab

Bbaug
Bb - D - F#

7th chords

A 7th chord is a 4 note chord consisting of a basic triad plus an extra note which is a 7th interval from the root note.
Not all combinations of triads and 7th intervals are ‘allowed’. See the table below. An X indicates that this combination is not ‘allowed’, all other entries are the chords that represent this combination.

7th interval

Triad
major 7thminor 7thdiminished 7th
majorM77X
minormM7m7X
diminishedXØ7 (m7b5)O7
augmentedaugM7XX

The following table contains the composition of the 7th chords and the table is built up similar as the the one with the basic triads above.

TypeCompositionNotationExample
Major 7thRoot -> Major 3rd -> Perfect 5th - > Major 7th(ROOTNOTE)M7 CM7
C - E - G - B

Ab
Ab - C - Eb - A
Minor major 7thRoot -> Minor 3rd -> Perfect 5th -> Major 7th(ROOTNOTE)mM7CmM7
C - Eb - G - B

F#mM7
F# - A - Db - F
Augmented major 7thRoot -> Major 3rd -> Augmented 5th -> Major 7th(ROOTNOTE)augM7CaugM7
C - E - Ab - B
Major minor 7th
(aka Dominant 7th)
Root -> Major 3rd -> Perfect 5th - > Minor 7th(ROOTNOTE)7C7
C - E - G - Bb

Eb7
Eb - G - Bb - Db
Minor 7thRoot -> Minor 3rd -> Perfect 5th -> Minor 7th(ROOTNOTE)m7Cm7
C - Eb - G - Bb

Am7
A - C - E - G
Half diminished 7thRoot -> Min 3rd -> Diminished 5th -> Minor 7th(ROOTNOTE)Ø7
or
(ROOTNOTE)m7b5
CØ7
C - Eb - F# - Bb

Em7b5
E - G - Bb - D
Full diminished 7thRoot -> Major 3rd -> Diminished 5th -> Diminished 7th(ROOTNOTE)O7CO7
C - E - F# - A

Bb
Bb - D - E - G