I’d like to illustrate the different compositional methods with a flower. (Flowers go well with music)
You are the creator of the flower and you have two options. You can either start the flower creation by initially forming the stem, or you can first build the bud.
If you form the stem first, you ensure that the flower will have a good foundation and structure, but the color and form of the bud will be limited. (Harmonic Method)
If you form the bud first, then you are free to color it and form it however you choose, but then you are left with the difficulty of creating a stem that can ‘fit’ the bud. (Melodic Method)
Harmonic composition is the art of creating an interesting chord progression to accompany a melody. In harmonic composition the chord progression would come first. For instance, someone might compose the piece below, and add on a melody later.
The harmonic method creates a framework for the composition and gives structure to the piece. Many popular song writers use the harmonic method for composing because it is much easier than the alternative melodic approach. The harmonic method is a great way to ensure your compositions are uniform throughout. However, if the harmonic chord progression is obsessively used for the song, the song can become boring. Consequently, it is a good idea to vary the harmonic chord progression throughout the song. Start with one chord progression, and then vary it up.
The harmonic method also limits what you can do with the melody. The melody is based on the harmony in the harmonic method, rather than the harmony being based on the melody. This creates a danger of constricting the melody. Even with the risks entailed with the harmonic method, numerous songs have been successfully composed using it.
Apologize (feat. One Republic) by Timbaland
Numb by Linkin Park
I Like to Move it by Reel 2 Reel (This is an example where the base can get monotonous)
There are many more examples.
Melodic composition is the art of creating an interesting melody without any restrictions. Once the melody is finished, the harmony is added. For example, one might have composed the melody below. This approach allows for more freedom in your compositions but leaves you with the difficult task of finding the right harmony to accompany the melody.
There are numerous ways to accompany the melody above. Finding the chord progression that fits the song can be a difficult task that can be eliminated if you use the harmonic approach.
Both the harmonic method and the melodic method for composing have their own drawbacks and strengths. If you are unsure which method you would like to use, then think of whether you like a catchy base or a memorable melody. If you like the base, then use the harmonic approach to create an unrestrained chord progression. If you like the melody, then use the melodic approach. Of course, you can also try them both :)