Practical Music Theory unit 7: Chord Scales (triads)

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  • Chord Scales - triads

  • Chord Scales (triads)

    A “Chord Scale” refers simply to all of the basic chords that are available in a given key or mode.  You can refer to the Table Of Major Scales to see the other keys, but for the following examples I’ll use the key of C Major.  This time, we’re going to number each step of the scale using Roman numerals–this is the common practice for identifying chords within a scale.  And I wrote out two octaves of the scale–you’ll see why in a minute.

    The I chord: major

    Using the concepts covered in the lesson on chord construction, we build a chord from each step of the scale.  The first chord, built from the first step of the scale, is known as the I chord (that’s a Roman numeral 1, so we just call it the “one” chord).

    I-chord

    We know that if we take the 1st, 3rd, and 5th steps from a major scale as-is, without flatting the 3rd or 5th, we have a major triad.  This will be true for any major scale in any key–the chord built from the first step of the scale will be a major triad.  So, we can say that “the I chord is major.”

    The II chord: minor

    Now we’re going to move to the second step of the scale, so in this case D.  We then apply the same concept to build a chord from this step:

    II-chord

    We know (refer to the table of major scales if you need to) that a D major triad is spelled as D-F#-A.  But in this case, we have D-F-A (no F#).  In other words, the 3rd has been flatted (lowered from F# to F).  You may remember that a flatted 3rd gives us a MINOR triad.  Again, this will be true for ANY major scale.  Therefore we can say, in general, that in a given key, the II chord is minor.

    The III chord: minor

    Now let’s build a chord from the 3rd step of the scale, the E:

    III-chord

    We know that an E major triad would be spelled E – G# – B.  But building off of the E in this scale, we get E – G – B.  So, again, the 3rd has been flatted–lowered from G# to G.  This gives us another minor chord.  So we can then say that the III chord is minor.

    The IV chord: major

    Now let’s look at the chord built from the 4th step of the scale (and now you can see why I wrote out two octaves of the scale):

    IV-chord

    An F major triad is spelled F – A – C (refer to the Table of Major Scales if you like).  And when we build from the 4th step of a C major scale, we also come up with F – A – C, a.k.a. an F major triad.  Therefore we can say that the IV chord is major.

    The V chord: major

    Now we’ll look at the chord built from the 5th degree of the scale:

    V-chord

    A G major triad is spelled G – B – D, and when we build the chord from the 5th step of the C major scale, we also get G – B – D.  Therefore we can say that the V chord is major.

    The VI chord: minor

    Now build the chord from the 6th step of the scale:

    VI-chord

    An A major triad would be spelled A – C# – E.  When we build the VI chord from the key of C, we get A – C – E.  So the C# has been lowered (flatted) to a C.  Like we saw with the II and III chords, this means we have a minor chord.  Therefore we can say that the VI chord is minor.

    The VII chord: diminished

    Finally, we’ll build a chord from the 7th step of the scale:

    VII-chord

    A B major triad would be spelled B – D# – F#.  But in this case, we get B – D – F, so both the D# and the F# have been flatted to just D and F.  Remember, from the lesson on chord construction, that a flatted 3rd AND a flatted 5th together make a diminished chord.  So we say, then, that the VII chord is diminished.

    Recap-the “chord scale” for C major

    So, going through all seven steps of the C major scale, and building triads from them, we get the following chords:

    I II III IV V VI VII
    C Dm Em F G Am Bdim

    This is known as the “chord scale” for C major.  Note that these are the triads–the next lesson will cover seventh chords.

    The chord scale in any key

    Like I have mentioned, we can take what we learned in this lesson, and apply it to any major scale, and come up with the following generalizations for all keys:

    I chord = major
    II chord = minor
    III chord = minor
    IV chord = major
    V chord = major
    VI chord = minor
    VII chord = diminished

    Be aware that you are by no means limited to these chords when you’re playing in a given key.  These are just the most basic chords that can be derived from the key.  But it’s entirely possible to have chords in a song that do NOT follow what we have learned here, so don’t be surprised when you run into it.

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