what is the difference between good and bad music


my friend says rap is bad music. another friend says mahler is a terrible composer.

is it all subjective, i.e., a matter of opinion ? or are there standards which can distinguish good from bad music, however one defines these terms ?

if there are standards, can one specify them or refer me to a source ?
mrtennis
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"Wine, women and song" is an expression that goes well together and, to me, beauty is in the senses of the beholder. Can you really set rules for greatness in any of these categories which are not, in the end, subjective? After all, each is entirely too complex to be absolutely defined or measured.
When I was in the USAF back in 73 I remember argueing the merits of rock vs country music with a co-worker from Texas. After a few discussions that went nowhere he said in his Texas drawl, "if don't say anything about my music, I won't say anything about that shit you listen to." That about sums it up for me.
I could send you the list of my music collection - it's pretty definitive as to what is good music. Some people disagree with me, but they're just idiots.