A big part of voice leading and counterpoint are cadences. Cadences are simply a way of ending musical phrases and ideas. There are a number of different cadences that happen in music. These are still just as relevant today although not used in exactly the same way. Today we're going to look at the different 'classical' cadences and see how they are used in today's music.
Following the Rules
When classical (i.e. classical, romantic, baroque etc.) musicians sat down to compose, there was a huge emphasis placed on voice leading and counterpoint. Classical musicians were preoccupied with the importance of the various independent lines, maintaining the voices and making sure there were no holes in their part writing (e.g. parallel 5ths and octaves). There were (still are) a whole set of rules that musicians would follow to make sure all of these things were taken care of. There were also other rules, like certain intervals (e.g. dim. 5th) and leaps that were to be avoided. Since the 20th century counterpoint has fallen out in place for more block and parallel lines. Most of the rules that were made for writing for band in the classical tradition were thrown out in the jazz era. Jazz musicians focused more on parallel lines, 'dissonant'* harmonies and swing. Voice leading though, is still an important part of writing and arranging in various styles.
*What at one time was considered dissonant (unpleasant, tense) may later be considered consonant (pleasing, no tension). It often happens that once people hear a dissonant interval or harmony often enough, it no longer is considered dissonant. Other general practices, (like always having to resolve suspended sonorities or ending on the I chord) no longer become particularly necessary. One of the trademarks of a innovator is someone who takes well known conventions and throws them out the window. Of course it helps if they do it in a musical and interesting way, instead of going against the grain just to be different.The Perfect Cadence
With voice leading, it's important that the individual voices move in the proper way. There are predetermined ways to end phrases and pieces. For example classical musicians would always end a piece with a perfect cadence (i.e. a V-I progression in root position). This had an element of finality to it that was the norm and part of the style. When writing out a V-I, there are a number of ways to arrange the four voices*. If it was in the middle of a piece, the cadence had to be voiced a certain way, if it was the end of the piece, it had to be voiced another way. If you're wondering why most of the symphonies you hear end in the same way (the big repeating V to I), this is why. Beyond the theory with the individual voices, to most of us a perfect cadence is simply a V-I chord progression. This is considered the strongest progression in music simply because as soon as we hear that V chord, we immediately want to go back to the I.
*Classical musicians would often write out their voice leading in four voices (separate lines). This was a convention that started early in Western Music and is still done today, even though we often hear sonorities made up of more than 4 voices.The Plagal Cadence
Beyond the V-I cadence, the other most used progression is the IV-I. This is referred to as the plagal cadence. Of course the voice leading rules that applied to the perfect cadence also applied to these. Whereas the perfect cadence had a finality to it, the IV-I progression isn't quite as strong. Where the perfect cadence felt more like a period, the plagal cadence was more like a comma. The IV almost feels like it could go anywhere; it doesn't have the strong desire to go back to the I. In this way the IV-I would often be used in the first part of a phrase letting the listener know that you weren't quite completely done.
The Imperfect Cadence
Whereas the perfect and plagal cadences both returned to the I, this cadence ends on the V. This cadence has much more of 'suspended' feeling. You are literally left hanging and seem to be waiting to hear the rest of the musical idea. It mostly stems from the strong urge of the V to return to the I. But in this case, it doesn't resolve.
Beyond the Basics
If you've studied music theory, you'll notice that these cadences are still the backbone of most of our music. There are books filled with 3 chord songs that use these progressions only. Don't be fooled by their simplicity, they're still very effective. If you're just beginning on your writing journey, don't be afraid to fully explore these basic progressions. They're effective because they work. Once you've gotten used to using these, you'll be able to use them in your own creations at will. Also, after using these for an extended period of time, you should be able to pick them out immediately in a song. Try listening to a song that has one of these basic progressions and see if you can tell what the chords are without your instrument.
So how can we use this in our writing? By knowing some of these conventions, we can use them (and go against them) at will. For example, try writing a short 4 bar phrase and end it with either a plagal or imperfect cadence. Notice how the music seems to begging for another phrase. Now write another phrase and this time end with a perfect cadence. See how the whole 8 bar phrase now seems like a logical sentence. Now that you know this, you can use this or go against convention on purpose. Try writing the piece but don't use any perfect cadences until your chorus. In fact try not to use the V chord at all. You'll notice that the cadence may have a different effect if it's only used once at a pivotal point (like at the end of the chorus) in the song.