Also, a lot of the sentences on music here are just not right. Jazz musician/composer here, who knows most of what music theory there is to know in a few genres

Also, a lot of the sentences on music here are just not right. Jazz musician/composer here, who knows most of what music theory there is to know in a few genres, which is not much. Most of the musical knowledge good musicians, improvising musicians at least, have, is private and unique to themselves, or stored in their bodies and muscle memory and even they don't "know" or understand it, they can just play. "Music theory" just doesn't take you very far at all. Shakespeare couldn't have explained what he was doing or how he did it, nor could Hendrix. They just could do it, natural as breathing, or like walking, which people can usually do without the help of theory or being able to explain how. > Even though the person might not be composing their own songs, their understanding of how music works likely makes them extremely comfortable playing and improvising any kind of song. Understanding music theory doesn't make you comfortable playing and improvising at all. Being able to play an instrument and improvise makes you comfortable doing that, which comes from doing them a lot. > if the person doesn't know the theory, it's likely that these songs are going to be hilariously bad. No, the songs of people who don't know music theory aren't hilariously bad. > To make it worse, musical progression is not a thing you just come up with -- songs aren't random, the chords for each song have a theoretical relation to each other. Making a decent song is a science, and one can learn it by understanding the theory. But a chord progression or melody or lyrics are often a thing people just come up with. Writing songs is in no way a science. You can't learn "making a decent song" by understanding music theory. The characteristic, memorable, wonderful moments in each song are usually the unique, irregular ones, about which there is no theory. Etc etc.