Parallel Motion
In general, there are four basic forms of contrapuntal motion that help design the pathways of each individual line, or voice. The first is parallel motion, a form of contrapuntal motion in which two voices move in a certain direction. Both voices move in the same direction (up or down) and by the same intervals. If you drew a line connecting the notes in each voice, you'd literally have two parallel lines.
Imagine that your soprano voice contained the notes G, E, C, E, G, upper C (the first six notes of the Star Spangled Banner, where you sing ''o-oh say can you see''). If you wanted your alto voice to develop in parallel motion to the soprano, you'd follow the same structure (down a third, down a third, up a third, up a third, up a fourth). So, if your alto voice started on A, the full line would be A, F, D, F, A, upper D. The structure is exactly the same, as is the interval between each note in both lines.
There's something you need to watch out for here. In our example, the two lines are a seventh apart (A to G is a seventh, F to E is a seventh, etc.). When building parallel motions, you want to avoid creating multiple notes in a row that have an interval of a fifth or an octave between the two voices. For example, if one line has a G, E, C, the line above it can't be D, B, G. Yes, that's parallel motion, but parallels of a fifth or octave are so similar that the voices become basically indistinguishable. We call this a parallel or consecutive fifth or octave. It's definitely something you want to avoid.
Similar Motion
But, what if you don't want to develop two voices with parallel motion? You could have them build in the same direction, but at different intervals. That's called similar motion. For example, both lines could be getting higher, but the intervals between the notes changes.
If we consider that line from the Star Spangled Banner of G, E, C, E, G, upper C, our motion is down, down, up, up, up. In parallel motion, our second line changed at the same intervals. But with similar motion, we could do something like this: A, F, E, F, G, A. The intervals between the lines changed, even if the direction of each voice stayed the same.
Contrary Motion
Now consider this: both voices move in different directions: one gets higher, while the other voice gets lower. That's called contrary motion. So, if the Star Spangled Banner has a motion of down, down, up, up, up, then contrary motion would create a voice that goes up, up, down, down, down.
Contrary motion doesn't have to maintain the same interval relationship between the lines, since the main emphasis is on the direction of movement. However, if you want to maintain the interval relationship between each note in the voice, you can. That's called strict contrary motion. So, if one voice goes up by a second, the other voice goes down by the same interval. As the relationship between voices is changing, this isn't a form of parallel motion. Instead, it's more of a mirrored relationship.
Oblique Motion
The last of the main forms of contrapuntal motion is oblique motion. Let's start with our star-spangled line of G, E, C, E, G, upper C: that's one voice. With oblique motion, our second voice would look like this: B, B, B, B, B, B, where one voice moves up and down and the other voice remains the same. You can play that stagnant voice as six independent notes, or as a single whole note. Either way, you have one voice establishing a drone or possibly a pedal tone, while the other develops melodically. As long as both lines get to where they're going, this is a perfectly valid form of motion.
Lesson Summary
Let's review. In four-part music, it's important to maintain the distinction between all four lines. This means paying attention to contrapuntal motion, or the movement between two lines relative to each other.
There are four main kinds of contrapuntal motion:
- Parallel motion occurs when both lines move in the same direction and at the same intervals. This is fine, as long as the sustained interval between the lines isn't a fifth or an octave.
- Similar motion occurs when two voices move in the same direction but at different interval.
- Contrary motion occurs when two voices move in different directions. If they're mirroring interval relationships, then we can call this strict contrary motion.
- Oblique motion occurs when one voice moves but the other remains the same.
By understanding these kinds of contrapuntal motion, you can develop all four lines while keeping each independent and distinct. Otherwise, your composition may just crash and burn!
