For these lessons I assume you have a basic understanding of music theory. If you don't, try out my lessons "pure theory."
Music: Organized sound
Composition: Work of music
Song: Composition involving vocals (notice the relationship between the words "song" and "sing")
Tempo: Speed of music
Rhythm: Area of music analysis and composition relating to time and it's interactions with other elements such as volume
Pulse: Repetitive rhythmic volume change (ex: 4 quarter notes, the loudest are the 2nd and 4th, you can hear and feel that "pulse" as if it were a heartbeat)
Accent: Note played loud/hard
Legato: Smooth, each note flowing into the next
Staccato: Each note played distinctively from the rest
Beat: Repetitive description of rhythm, pulse, volume, dynamics, and/or theme through use of instruments that don't create "notes" (such as a drum set or other percussion)
Melody/Tune: Most easily described as a phrase or collection of musical notes played in succession
Harmony: Analysis/composition concerning chords
Chord: 3 or more notes played at the same time
Chord Progression: Series of chords
Counterpoint: Analysis/composition concerning the interactions of different melodies heard simultaneously
Polyphonic composition: "Many voices;" composition resulting from counterpoint
Homophonic composition: "Same sound;" composition resulting from harmony
Monophonic composition: "One sound;" composition resulting from 1 voice (instrument)
Voice leading: Arrangement of "voices" and their interactions
Voices: Different entities used to create sound in composition (saxophone, violin, vocals, etc.)
There are many ways in which one can go about composing, but I'm going to offer a simple step by step process for now:
Step 1: Inspiration
Step 2: Purpose
Step 3: Theme
Step 4: Development
Step 5: Structure
Step 6: Review
A lot of people go out of their way to be inspired; they often don't understand that the very reason one should make music is because they are inspired, not the other way around. If you have no inspiration, don't try to write music, because it won't be an HONEST sound, it'll be a sound you forced. Don't go travelling around the world for inspiration for music making. Instead, travel around the world just for the sake of doing it, just because it'll be fun and you want to do it and you want to make discoveries about yourself and the world around you. Then, once you're done travelling, you'll want to write music that expresses your feelings about the experience. If you're not inspired, you don't have writer's block...The real problem is that you aren't living a very fulfilling life. And if you aren't inspired, why do you want to write music so badly anyway?
Make sure you understand why you're making this music and what you want the music to do. Example: "I'm writing this song because I want to communicate the emptiness I feel from my lover leaving me and I want the music to sound isolated and hollow." Just like inspiration, don't go looking for purpose. If you don't have a purpose for making music, don't make music! There's just no purpose without...Purpose...And be HONEST with yourself. If your real purpose is to write a catchy hit that'll make you a lot of money, don't hide that from yourself. If that truly is your goal, there's a certain way of going about it and you aren't going to achieve it if you aren't honest about the goal. Any purpose is valid. "I want to write a silly song about flatulence to make myself laugh." "I want to write that song to make OTHER people laugh." "I want to write a song for my girlfriend on Valentine's Day." "I want to express the feeling of unity and harmony with the universe and all of existence." "I want to explain that acid trip that was just too crazy for words."
The theme is usually the lead melody (vocals, guitar, saxophone, etc.), but in modern music it can be anything from a guitar riff to a funky bassline. In rap music, the theme is often a beat, or a repeated lyrical phrase. The theme should express your inspiration and fulfill your purpose. The theme in The Beatles' "Eleanor Rigby" is the vocal melody, during the line "Ah, look at all the lonely people." The theme of Led Zeppelin's "Black Dog" is the catchy guitar riff. Think of the theme as the first part of the song that is actually written...A tune or idea that you can develop and write the whole song based around.
This is the part where you may notice true writer's block, and that can be frustrating. The best way to handle it is to just plow right through: KEEP TRYING. You could be working on a dozen themes at once that all sound horrible to you and then weeks later just one of them has grown on you and you have a direction to take it in. Just keep working and keep trying until it works.
This is the part where you experiment with the theme. See what works, what doesn't work, what fulfills your purpose, what expresses your inspiration, what's too much, what's too little, etc. Try playing your theme backwards! Try writing another theme that disagrees with the first (like in The Beatles' "Lucy in the Sky with Diamonds, the verse and chorus sound like almost opposite worlds). Try adding lots of variations to your theme (If your theme is the melody C, D, E, try playing C, D, F for one of the measures for a feeling of suspense or tension, then relieve that by playing the original melody again). Experiment, and don't through any ideas out until you've started working on the structure.
Figure out how everything works rhythmically, and when exactly you should use the variations you came up with in your development. Make sure you understand how the theme works rhythmically in each measure; understand the pulse, time signature, etc. Also take into consideration the larger structure of the overall composition (for example, the pop song structure of intro-verse-chorus-verse-chorus-bridge-chorus-outro). You may discover during this step that you've only written material for a chunk of the song (say, the verse) and that you need to start this process all over to write other chunks (say, the chorus). This can be avoided in songs that are very melodic and very well-developed; in the development stage you could have written the lead melody for the entire song, leading smoothly from verse to chorus and so on, but this isn't possible all the time because sometimes your purpose or inspiration require you to write opposing themes for each section of the song. This step is where your individual style starts to shine through.
Think carefully about your purpose and inspiration and mess around with your song. A minimalist composer may get to this step and realize that the rhythm section to the song has too many variations, and that the theme isn't properly expressed because it's muddied up by all the crazy things the voices around it are doing. A metalhead, on the other hand, may decide that the beat wasn't loud enough, or that there should be some insane shredding over the breakdown. Ultimately, it all depends on the inspiration, purpose, and style.