What about the usage of specific words in black metal lyrics across time? Have common terms – like life or death – been mentioned in a constant fashion through the years, or has their frequency changed dramatically?
The figure below plots the frequencies of a few selected words against time (in years). I’ve chosen death, life and time because they are among the most frequent terms in the whole lyrics data set. As for god and satan, well, if you don’t know why I picked them then that probably means you’re not acquainted with black metal at all, so I’ll refer you to Google or the nearest (decent) record shop to sort that out.
I’ve bundled a few synonyms and hyponyms with each term, taken from WordNet. This means that, for example, the occurrence count for satan also includes the counts of similar terms such as lucifer and devil.
Looking at the plot we can see that death was at its highest point around 1998 and has been decreasing since then (being surpassed by life in 2006/07), up until 2012. And notice how satan closely follows god across the years. This probably means that most lyrics than mention one of these entities, also mention the other.