Grade Six Music Theory - Harmony Lesson 7: Harmonising a Melody (2)
Step 4: Chords & Inversions: Creating a Bassline
When you decide which inversions of each chord to use, you are in fact creating a bass line. The inversion of a chord tells you which note is in the bass - so each time you pick an inversion to use, you are creating the next note of the bass line.
In the grade 6 exam, in question 1(a), you don't have to write out the bass line at all - does that sound like a relief? Well in fact, it's not such a good thing! You still have to know what your bass line looks like and how it functions harmonically, whether you write it out or not; and it's much easier to spot mistakes when you are looking at actual notes rather than just Roman numerals.
We strongly recommend writing out the notes of your bass line in order to avoid serious errors. (You can rub them out before you hand in your exam paper!)
Take a look at some of the rules you have to follow:
Rules
Your bass line must not break these basic rules of harmony:
The bass line must, of course, fit the notes of the chord you've chosen.
Click on the links to learn more about these rules, then come back to this page when you're ready. (Don't worry if you can't remember everything just yet - practise makes perfect!)
Guidelines
You can use either the root or the third of the chord in the bass. This means you can use root position (a) or first inversion (b) chords.
Root position chords are stronger (more stable) than first inversions, so always use root position chords at a cadence.
Try to use "contrary motion" in relation to the melody line. That means if the melody line goes up, then the bass line goes down, and vice versa. Don't worry if you can't always manage contrary motion, but you should always aim towards it!
It's important to realise that there isn't only one right answer when harmonising a melody. You can choose whichever chords you like the sound of, as long as you don't break any rules. Bach himself often harmonised the same melody in lots of different ways, just for fun!
You can only use the 5th of the chord in the bass (second inversion or "c" chord) in a cadential or passing 6-4 - be careful! In the following instructions, we won't try to include second inversion chords. Try them for yourself only when you feel confident to do so! There are some instructions at the bottom of this page.
How to Choose Chords and Inversions or "Writing the Bass Line"
Here are the triads in order of how common they are, (e.g. I is the most commonly used chord, but iii is quite rare), and then the triads which most frequently follow them (e.g. chord iii is almost always followed by chord vi, but chord I can be followed by any chord at all).
Any chord can also be followed by the same chord, as long as it's in a different inversion. For example, Ia is often followed by Ib.
Major Key Signatures
I
any chord
V
I, vi
IV
I, V, ii, vi
ii
I, V
vi
ii, V, IV
viio
I
iii
vi, IV
Minor Key Signatures
i
V, iv, ii?, VI
V
i, VI
iv
i, V
iio
i, V
VI
i, iv, V
viio
i
iii+
avoid
Using the table above, and what we know about common chord progressions, let's get to work and pick some chords for our melody.
Start with the first note. Choose a chord from the three you noted down, and pick the inversion: root position or 1st inversion. Start by choosing the most common chord i.e. Ia, if possible. (You can change it later if you need to).
Lightly pencil in the bass note. (We say "lightly", because you'll probably end up doing a lot of rubbing out!)
For the next note, there are 4 or 6 possible chords (two or three chords x two inversions). Go through each possibility and eliminate chords which break the rules and don't follow the guidelines. (If all the chords break rules/guidelines you'll need to go back and choose a different first chord).
You need to check each possible chord against the previous one, looking for consecutives and illegal intervals.
From your "good" chords, choose the most likely chord. The primary triads are I, IV and V.
Repeat for each note of the melody.
If you find yourself "stuck" i.e. all the chords break rules, you'll need to go back one step and choose a different chord. Double check that the new chord doesn't break any rules!
It's ok to have a little bit of similar motion - but try to avoid it as much as possible!
Chord 2 Here are our 6 choices for the second chord:
ia - repeat of the first chord - not a great choice ib - similar motion - not a great choice iva - consecutive 5ths - not allowed ivb - good choice VIa - good choice VIb - bassline doesn't change - not a great choice
ivb is a primary triad - so let's choose that one. (You could choose VIa if you prefer.)
Chord 3 We have only 4 choices for chord 3, because we don't use III+ in grade 6:
Va - similar motion. Vb - not allowed for two reasons: Ab to B in the bass is an augmented 2nd, and there would be a doubled major third/leading note. viia - not allowed because diminished chords are only normally used in the first inversion, and you may not double the leading note. viib - not allowed because the bass would move by an illegal augmented 4th.
Although Va gives us similar motion, it's the only chord which is allowed, so that's the one we'll use.
Chord 4
ia - similar motion. ib - low Eb is extremely low, and high Eb involves a big leap and similar motion. Not a great choice. iva/b - the progression V-iv is not recommended (see the table above) VIa - similar motion VIb - similar motion (note that the doubled major third is allowed in a V-VI progression)
We'll choose ia, because it's the most common chord.
Chord 5 iia - ii is diminished, so it should only be used in the first inversion. iib - ok with a low F in the bass Va - ok with a low G in the bass Vb - ok viia - not allowed in root position viib - similar motion
We've got three potential chords - iib, Va and Vb. We are also just about to arrive at the cadence we've already put in. So, we need to check our chords not only against chord 4, but also against chord 6 (ia):
iib - ok but bass line seems to jump about a bit too much Va - ok, but the bass line would be a repetitive G-C-G-C-G! Vb - good - the bass line moves by step, the leading note B in the Vb chord will resolve on to the tonic in ia.
Choice: Vb. We'll put in the bass notes of the cadences too:
Chord 8 After a cadence, a new phrase starts. Moving by step and in contrary motion from the previous chord is less important here.
ia - ok. ib - large leap in the bass. VIa - consecutive 5ths - not allowed. VIb - large leap in the bass.
Choice: ia.
Chord 9 ia - repeat of previous chord ib - ok iva - ok ivb - similar motion VIa - similar motion VIb - cannot double the major third - not allowed
I'm going to choose ib, because I prefer the bass line it creates.
Chord 10 iva - not allowed as it creates an exposed octave ivb - ok iia - not allowed as it's diminished iib - exposed octave again viia - not allowed as it's diminished viib - ok
I haven't used a chord vii yet, so let's use one now for the sake of variety. (A vii chord functions like V7 aurally.) Choice: viib.
Chord 11 Chord vii should only resolve to chord i. (See table above.)
ia - similar motion ib - ok (it's ok to double a minor third)
Choice: ib
Chord 12 As before, we should consider this chord not only in relation to chord 11, but also to chord 13 in the cadence.
Va - chord 13 is Va, so it's a repeat. Vb - the bass cannot move by a diminished 4th here. (A diminished 4th is a dissonance; the note which follows a dissonant interval must occur between the two dissonant notes. i.e. be a note between Eb and B natural. A note B in chord 12 would have to rise to C in chord 13. The bassline in chord 13 is G, which is outside the interval Eb-B.) iia - not allowed - diminished chord iib - bad choice because the bass would have a leap of a 7th viia - not allowed - diminished chord viib - not allowed - consecutive octaves
Houston, we have a problem! None of our chords are allowed!
This kind of stalemate scenario happens all the time when you try to harmonize a melody. I've deliberately included it here, to help you figure out what to do next - read on!
What to do when you get stuck!
When you get stuck, go back one chord and read through your choices again. Could you have chosen a different chord? If not, go back another chord and keep going back until you get to a point where you had a choice of good chords.
Cross out the chord you chose first time round and make a note that it causes problems further down the line. (It's a good idea to do this, in case you end up re-tracing your steps yet again, and forget which chord you chose first time round!)
Choose the next best chord, rub out everything you had written up to but not including the cadence, and repeat the process as before.
We need to look at chord 11 and see if there is another possibility. We're in luck! Chord 11 could also be ia. Let's test the new chord 11 against chords 10 and 12:
Va - repeat of chord 12 (as before) Vb - similar motion iia - not allowed iib - high F makes a leap of a 7th down to G, and low F is similar motion (and the second in a row, which is even worse!) viia - not allowed viib - ok
Thank goodness! We only had to change one chord, and it meant we now have one good chord and 2 not-so-good-but-ok chords to work with. Choice: viib.
Note: when a piece is in a major key, it's completely possible to harmonise every note simply using the major chords I, IV and V. However, you will create much more interest harmonically if you throw in one or two minor chords - ii and vi most often.
What About Second Inversion Chords?
Second inversions can be used in passing 6-4 and cadential 6-4 progressions.
Passing 6-4s are pretty tricky to get right, so basically we don't recommend trying to use them in this question (1a of the grade six paper).
Cadential 6-4s, on the other hand, are pretty neat things to use if you can manage them. Look at the chords you've picked, and see if the pattern I-V-I crops up at a cadence. If it does, then you can safely write a cadential 6-4 using Ic-Va-Ia.
The Final Answer
Your final answer should have the Roman numeral letters with their inversions. You are also allowed to write out the full chords instead of using the Roman numeral system, but I advise against this. If you write out the full chords, you should make sure that every single part conforms to all the rules of harmony. If you write the Roman numerals, the middle parts are left blank and you don't need to worry about any rules for those parts.
Here's our final answer: Click to play -
Just for fun, I filled out the middle parts and made the last chord major (a "tierce de Picardie") - click to listen:
