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25: Tonic Function

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Lesson 25: Tonic Function

This lesson teaches the different effects of the different major-key diatonic triads.

Before taking this lesson, you should know:
To review, the common major-key diatonic triads are:
I   IIm   IIIm   IV   V   VIm
This lesson explores the tonic function chords: I, IIIm, and VIm.

The I Chord

Let's start with the I chord ("the One chord"), also called the tonic chord. ("Tonic" is another name for the 1st note, or "degree 1", of a scale; that's where the term tonic chord comes from.) The tonic chord is the home chord in a song's key. When the tonic chord is playing, it feels like you're "at home" or "at rest"; when any other chord is playing, it feels like you're not "at home" (with some partial exceptions we'll get to below).

Musical phrases often start or end (or both) on the tonic chord; if a phrase doesn't do this, then the whole phrase tends to feel "not at home", and it's likely to be preceded and/or followed by phrases which do start or end on the tonic chord.

The VIm and IIIm Chords

The I chord is "the" tonic chord, but two other diatonic triads also have tonic function; that is, they have an "at home" effect similar to (but weaker than) the I chord. These "substitute tonic" chords are:
  • VIm
  • IIIm

Why do the VIm and IIIm chords have a "tonic" effect like the I chord? Basically, because they share most of the same pitches. For example, in the key of C:
I = C = (c e g)
VIm = Am= (a c e)
IIIm= Em= (e g b)

The VIm chord. Of these two substitute tonic chords, VIm is probably "stronger", for a couple of reasons:
  • It contains the "tonic pitch" of the song's key (e.g., in the example above, the Am chord contains the pitch "c", which is the tonic pitch for the key of C).
  • The VIm chord is also the Im chord (the tonic chord) of the relative minor key to the major key we're in. In the example above, the Am chord is the tonic chord in the key of A minor; the key of A minor is the relative minor key to the key of C major. (See Lesson 28: Natural Minor Scale, which leads to relative minor keys.) In fact, you can make a major-key song temporarily sound like it's in its relative minor key, just by using the VIm chord (instead of the I chord) as the "home chord" in that section of the song. This is actually a very commonly-used effect.

The IIIm chord has a "weaker" or more "passive" tonic effect, probably because it doesn't contain the tonic pitch (in the example above, the Em chord does not contain the pitch "c"). I usually see the IIIm chord used in a song for one of these reasons:

Mixing Tonic and Non-Tonic Chords

The "dance" between tonic and non-tonic chords in a song is a fundamental aspect of the song's musical effect. If a song stays on only tonic chords for a long time, the effect is "static" or "monotonous". If a song stays away from tonic chords for too long, the effect is "wandering" or "lost".

This "chord function dance" is just one of many techniques for using an even more universal principle in music: tension and resolution. Tension is when the music feels "unsettled" (e.g., non-tonic chords); resolution is when the music feels "settled" (e.g., tonic chords). Moving from tension to resolution is one of the basic principles for creating musical pleasure.

Next, go on and learn about the other diatonic chord functions in Lesson 26: Subdominant & Dominant.

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1: Introduction
2: Practicing Songwriting
3: Pitch Names
4: Letters Game
5: Sharps & Flats
6: Half-Steps
7: Whole-Steps
8: Steps Game
9: Scales
10: Major Scale 1-2-3
11: Major 1-2-3 Games
12: Major Scale 1-5
13: Major 1-5 Games
14: Chords: Major Triads
15: Major Triad Games
16: Minor Triads
17: Minor Triad Games
18: Major Scale 1-8
19: Major Scale Games
20: Keys
21: Roman Numeral Chords
22: Scales Above 8
23: Diatonic Triads
24: Using Diatonics
25: Tonic Function
26: Subdominant & Dominant
27: Diatonic Function Analysis
28: Natural Minor Scale
29: Natural Minor Games
30: Minor Key Triads
31: 7th Chords
32: 7ths Games
33: Melody: Chord Tones
34: Treble Staff
35: Treble Staff Game
36: Time: Beats & Measures
37: Note Lengths
38: Tied & Dotted Notes
39: Rhythm: Rests
40: Non-Root-Bass Chords
41: Major Pentatonic Scale
42: Embellishing Tones
43: Melody Rhythm: Rolling Stone
44: Pitch & Frequency

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