Heavy metal lyrics are the words used in songs by heavy metal artists. Given that there are many genres of heavy metal, it is difficult to make generalizations about the lyrics and lyrical themes. In 1989, two metal scholars wrote that heavy metal lyrics concentrate "on dark and depressing subject matter to an extent hitherto unprecedented" in any form of popular music. Jeffrey Arnett states that metal songs are "overwhelmingly dominated" by "ugly and unhappy" themes which express "no hope" for the future.