Sometimes philosophy, sometimes poetry, other times heavy metal. Core sucks don't bother with it but real metal sub genre's?, well when black sabbath came out, along with a few others, the formula of heavy metal wasn't quite right yet ergo proto-metal, definitely heavy metal but not quite right yet, not yet complete. Proto-metal comprised of heavy blues, hard rock and r&b also featuring more extreme guitar techniques than standard rock such as heavy tremolo picking, shredding, etc, also heavier than normal distortion amplifiers.
The next evolution was NWOBHM
the genre that got metal right, eliminating the r&b element altogether and adjusting the heavy blues hard rock fusion for less blues and more rock and more melody than one might expect, notable bands include Iron maiden, Judas Priest, Motorhead, etc. From this we go two ways commercial/glam metal which take it or leave it is OK,
and apm american power metal,
Commercial/glam metal nearly killed metal altogether by being to ridiculous in the theatrics department but had a nice sound to it and it was stupidly fun to listen to, it had more in common with proto-metal than it did with NWOBHM even though a NWOBHM band called def leopard started it. Thrash bands just wanted to play NWOBHM but fast like a lot faster and with a much harder picking technique resulting in a sound that made it seam like the guitars were growling at you, the musical equivalent of a particularly vicious bar fight, notable bands include Megadeth, Metallica, Slayer, Anthrax, Testament, Annihilator, Exodus, etc, at the same time there was apm and it was just Americanized NWOBHM with more attitude and more machismo, it was a dead end for metal though and went nowhere in terms of musical formula's constant evolution, but it was perhaps critical to the development of american heavy metal as a whole, notable bands include Metal church, Armored saint, etc. Thrash however led many places such as Death metal and Black metal. Before we get to them however i will take this time to also refer you to two smaller movement's worth examining #1. Neo Classical metal i.e. Heavy metal+Classical music.
#2. Progressive metal i.e. Heavy metal+progressive instrumentation.
#3. Epic Metal i.e. Heavy metal with longer intros and bigger more grandiose sounding riff's.
Black metal and Death metal, the proverbial two sided coin of the rather unfortunate extreme metal movement, i say unfortunate because of all of the murder and bickering within it, especially within Black metal but as to their formula, Death metal was created by the thrash band Death who removed the harder picking technique and took the harsh vocal's from thrash to the next level thus creating "Cookie monster" growling vocal's also they played big powerful sounding chords and riff's the musical equivalent of a gut punch, which i find exciting, notable bands include, Cannibal Corpse, Opeth, etc. Black metal also removed the hard picking technique of thrash and Added a more melodic sound, you in fact can have a shit tone of melody in Black metal, however the point of Black metal is to sound either very dark or very evil so the melody must be in all minor chords, no major aloud XD, The vocal technique is a growl described as "Donald Duck" and the drums where taken to the next level as well, instead of thrash drums they sped up the drumming as well to include such techniques as Blast Beating, Black metal is very spiritual and almost exclusively religious in nature mostly satanic but also pagan and even christian, notable bands include Venom, Marduk, Burzum, Behemoth, Dimmu Borgir, etc.
NWOBHM also spawned epm or European Power Metal.
epm would have the same relative tempo as thrash but just be really fast NWOBHM with quires and keyboards, Notable bands include, Helloween, Primal Fear, Firewind (not with Apollo he sucks), etc.
From epm we get,
#1. Folk metal i.e. epm+ethnic folk music of Europe.
#2. Viking metal i.e. epm+heavier riff's and classical viking chant and Norse themed lyrics sometimes growls.
More Notable smaller movements such as,
#1 Goth metal i.e. Heavy metal+Gothic moods and subject matter, thus effecting the melody and sound.
#2 Fringe metal i.e. Heavy metal+some other foreign musical element's not from rock'n roll.
#3 Doom metal i.e. like scary black sabbath but all the time.
#4 Djent i.e. Heavy palm muted guitar playing (is very controversial).
#5 Sludge i.e. Heavy metal with very dirty, grungy sounding Heavy riff's.
The next evolution of metal lies with Black metal and Death metal.
When we reintroduce the thrash hard guitar picking technique to Death metal and then speed up a bit we get slam i.e. Abominable Putridity, and when we inject melody we get Melo-Death=Melodic Death metal, and when we speed up and grind the guitar pick some we get Goregrind, And when we make the guitar techniques super difficult we get Tech-Death=Technical Death metal. If we wan't the true Heavy metal, not core to continue to evolve we must find a way to mess with black metal's formula to create a new sub genre just like we did with Death metal, perhaps reintroducing the harder picking technique of thrash like we did with Death metal may have an answer, this would create a much more aggressive sounding Black metal, perhaps we could call it Demon metal, but due to the ma liable nature of Black metal's formula all we get is just adding it to preexisting formula's, if we want to evolve metal further we must manipulate Black metal's formula next. Thank you for reading, please follow me on both minds and Steemit.