Four Part Writing

Hey guys, welcome to 12tone. Today we're going to talk about four-part writing. What is four-part writing? Well, the name kind of gives it away, doesn't it? More formally, four-part writing is a form of classical composition still taught today in which harmony is formed through the interplay of four distinct parts, also called lines or voices. Four-part writing is unlikely to come up in your day-to-day musical experiences, but it's a great lens through which to look at theoretical ideas, and learning to think in four-part writing is incredibly valuable in understanding harmony not only vertically in chord voicings, but horizontally through voice leading. Here, for instance, is a simple four-part piece of my own composition. For general purposes, we tend to refer to the four parts as the four major choral voice classifications, soprano, alto, tenor, and bass. But that doesn't mean we have to be writing for voices. It could just as easily be a string quartet, four horns, or even just a single piano. However, thinking of them as voices gives us a good frame of reference for range, so we use those. These voices can move between chords in four ways relative to each other. First is static motion, where neither voice moves, as in the alto and soprano in this example. Second is oblique motion, where one voice stays the same while the other moves, as seen between the tenor and, well, everyone else here. Third is contrary motion, where one voice moves up and the other moves down, as seen between the bass and soprano here. Fourth is similar motion, where both voices move the same direction, either up or down, like the tenor and soprano here. A subtype of similar motion is parallel motion, where the two move not only in the same direction, but by the same interval. Be careful, this can be dangerous. More on that later. Four-part writing is defined by a set of rules that specify how the voices can move relative to each other. The first of these is spacing. We don't want the voices to be too far apart. The rules state that no two consecutive voices can be more than an octave apart except for the tenor and the bass. This exception is because, while the upper voices tend to move smoothly, mostly by steps, the bass may need to jump very large intervals suddenly to ensure proper inversion. The second major rule is called crossing. We never want our voices to cross. What this means in practical terms is that in any given voicing, from the bottom to the top, we want the bass, then the tenor, then the alto, then finally the soprano. A voicing like this, where the alto goes below the tenor, isn't allowed. We also have to watch out for crossing voices in between chords. If the alto is on A here, the soprano can't go down to G in the next voicing, even though the altos move down further. The third rule is doubling. This is more flexible than the others, and you'll find scenarios where you don't bother with it, but it's a useful framework. Since especially older classical music is very triad-based, we'll often only have three unique notes to give to our four voices. This means that in any triad voicing, two voices will be singing the same note, although not necessarily in the same octave. The rule here is that you want to double the most stable note in the chord. In root position, this is almost always the root. In first inversion triads, however, things get more complicated and depend on the chord's function. A simple rule of thumb, though, is to double the chord tone that is either the tonic, the fourth, or the fifth degree of the key, whichever is in the chord. However, if voice leading requires something else, you should feel free to do so. Second inversion triads always double the bass, but that's because second inversion triads have very specific uses in four-part writing, which we'll cover in a later video. One incredibly important rule, though, is that you should never double the leading tone in a dominant function chord. Why? Well, that brings us to the last of the four primary rules, the dreaded parallelism. One of the defining features of four-part writing is the shared prominence and smooth interplay of the voices. While the soprano may nominally be the melody, each voice serves an important, independent function. However, certain types of motion can weaken that independence. When two voices move parallel to each other, this makes one voice sound like a mere echo or copy of the other, weakening it. This is especially noticeable when the voices are very consonant intervals apart. For this reason, we avoid parallel motion between voices when those voices are a perfect fifth or an octave apart. This is true regardless of which actual octave the notes are in. We only care about the note name. So if we have this voicing, and the bass moves from F-sharp to G-sharp, the alto, also on F-sharp, can't also move there. Likewise, the tenor on C-sharp can't move up to D-sharp. To combat this, we have two basic rules of thumb. First, we try to keep common tones wherever possible. If a note is in both chords, the same voice should sing that note in both voicings. Second, when the bass moves by step, all three of the upper voices should move contrary to it. So if the bass goes from D up to E, then the tenor, alto, and soprano should all move down. This way, you get all the appropriate chord tones with no parallel motion. And that's four-part writing. We'll be talking a lot more about this in the future, but until then, keep on rockin'.