I have some college education on music and music theory. For any composer I highly recommend looking for and buying "Tonal Harmony – with an introduction to twentieth-century music" by Stefan Kostka, seventh edition. (isbn: 978-0-07-802514-3 ).
That book is chock full of information and any level of composer would benefit from reading it. One of the interesting things I learned had to do with melody. Melody in today's music is often overlooked, not only in pop but in other common genres like rap, synthwave, chill-hop, electronic, and virtually every genre excluding jazz and classical.
This isn't a rant on "how terrible music is nowadays! Ooohooho nOoooo." Rather it is pointing out certain rules of melody writing and pointing out that most songs nowadays do not follow those rules.
The first rule of melody of western tonality I would like to discuss is shape. According to western tonality,
a melody should have a clear yet interesting shape to it. A melody without a shape would be one note type melodies. If you were to draw that out, it would be a flat line. Now, flat lines are pretty boring so not only are one note melodies boring but melodies that only ascend or descend are also uninteresting.
Old composer melodies are actually fantastic examples of this. Bach, Mozart, etc. Here's one from bach.
Here's the lines but exaggerated a little for clarity
This shape as a melody shape is much more interesting than just flat lines. yet, they aren't complex. If you had to look at the shape for 10 seconds and then turn around to draw it from memory, everyone could easily accomplish that.
For most melodies found in pop music, there is either very little shape or they violate the second rule I will talk about.
The second rule has to do with the melody having
a single focal point. And a focal point is simply
the highest note in a melody. Looking at the above melody you'll see that it follows this rule as well. Bear in mind that while there are 2 lines, in reality it is one melody. The focal point for that melody is in the second line and it is a D. There is no other note higher than that D and no other D exists in the melody making that high note the focal point. (of course bach gets pretty close with multiple C's but there is only one D).
In today's music, especially pop music, this rule is completely left out. Many many melodies in tunes played on the radio have no focal point, no highest note, unless it's the end of the song where the singer jumps up an octave to make a huge finish.
Take for example the melody to Shawn Mendes' 'senorita'. For the main melody, if I counted right, there isn't one focal point. In fact there aren't 2, there aren't 3, and there aren't 4. There are 9 focal points. . . . which makes it so none of the high notes are actually focal points . . . meaning the song doesn't obey the rules of western tonality because the melody has one high note which it repeatedly comes back to but never goes above.
(I will not have a picture to demonstrate because of copyright reasons)
The biggest problem I have with this fact is that that song, senorita, topped the charts a while ago cementing it as a huge success and widely popular. But the song doesn't follow the rules of western tonality. So for aspiring musicians and composers of our time, many will listen to these songs and assume that having no focal point and having a shapeless melody is a correct way to structure a melody.
Some might ask, "well, why exactly is that bad?" And this question is mildly difficult. The best answer I have is that we have these various rules for a reason. That reason is mysterious to me but I do know that when humans create music they mostly all end up following these and other rules whether or not they even consciously know them. The reason to follow these rules is because they add structure, they help to avoid monotony,
they make your music sound good.
That being said, music is of course an art form. And art, being subjective and totally controlled by the creator, is subject to the artists wishes and desires. If you as an artist want your music to have a good deal of repetition (like most pop music), or if you want it to have structure (by using these rules), etc, then do it. Nobody is stopping you. The only advice I have is to say that when creating a piece of music or a song, keep in mind your purpose. They 'why' of it all. "why do I want the melody to go up at this point?" "does that further the purpose or message I'm trying to get across with this piece?" "What does having one versus many focal points convey to the audience."
Really what I want is for people to think.
Don't do/create because it sounds cool. Do it for a purpose and really think about every aspect of your music.