Music should not be looked at as a whole. It is simply a combonation of notes and chords, mixed together.
Why do we have songs stuck in our head that we like/don't like? Probebly because of the sub-concsious mind. Take the song 'Cars', by Gary Numan, for example. 'Cars' was his biggest hit; he had no other actual hits (go with me here). It's considered one of the best 'One Hit Wonders'. Because of it's thereforth popularity, we have it go through our minds constantly because of us wantin' to be like everyone else.
Or, because of the actual notes. 'Fur Elise; (For Elise), by Beethoven (1770-1827), is very popular, even today (for classical music in general, that is). Most people can easily regonize nine note main meleody, but have no idea what the song is called. It's even used in a lot of rap songs today. And guess what; if you've never heard the song before, and you were familiar enough with music to recognize the note to the sound it produces, you would look at the actual sheet music for 'Fur Elise', and even the most advanced muscians would think it would be the worst song ever. An Eb between to E naturals. It's a natural 'don't' of music.
'Stairway to Heaven', by Led Zeppelin (A zeppelin is something like a blimp. Led = lead, so a lead blimp O_o (that was sorta off-topic)), contains plenty of chord changes and stuff, and it's one of the most popular classic rock songs in history.
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Why do we recognize "chord" as different from "dischord" or that sharp is not on key, and neither is flat.
Thats sorta like tellin' the difference between major and minor chords. Major, in simple terms, means joyful sounding. Minor, in simple terms, means horror sounding. Most songs and easily be divided as either major or minor. 'Oh Blah Di, Oh Blah Da', by The Beatles, can easily be considered a major song. On the other hand, 'Tocatta In G', by Bach, can easily be considered a minor song. 'Tocatta In G' is the same or more popular as 'Fur Elise', but yet the majority of people can't name the song; just recognize they've heard it before; 'your brain remembers what you forget'.