My adventure-espionage novel A Place of Brightness describes a secret Communist group that organized an underground insurgency to attack the newly democratic Romania. The twin sons of a woman who once fought in an underground anti-communist insurgency are pulled into the action and help a Romanian agent in her attempt to foil the communist plans.
But in the course of writing this novel, I had to familiarize myself with the confusing rules governing capitalization of the words communist and communism.
To help future writers and researchers, I will summarize the rules here and show you examples of each case using quotes from my book. There are a number of somewhat varying and competing systems out there, so don't be surprised if you see minor disagreements within the style sheets of specific organizations.
1) (A) The noun communism is not capitalized (except, of course, (B) at the beginning of a sentence). This makes sense because, even in the height of Soviet power, communism was an idea, not a single unified political entity.
Example (A): “The day you were born Grandma told us about her premonition. She said that one of your sons would end communism once and for all.”
Example (B): Suddenly she opened her eyes wide. “Petre,” she gasped. “Communism will fall.”
2) The adjective communist is capitalized when it describes (A) individuals as a substantive or (B) attributive adjective, as well as when applied to (C) governments or formal groups.
Example (A): “We’re only fifteen,” Stefan stammered. “What good can we be against all those Communists?”
Example (B): “What do you make of this?” Victor asked. “Is she just crazy? She looks like she could be my grandmother. A secret Communist spy? Really?”
Example (C): “In the last months, Poland, Czechoslovakia, Hungary, and East Germany have peacefully overthrown the Communist governments there. Romania is the first to do so in a bloody revolution.”
3) The adjective communist is not capitalized when it describes (A) communist ideology as applied to abstract concepts apart from individuals, governments, or formal groups It is also not capitalized when used as a (B) predicate adjective.
Example (A): She looked up at the men seriously, brushing dyed-red hair from her eyes. “The long term plan is the restoration of communist rule in Eastern Europe.”
Example (A): “Smart thinking, not giving your personal cell number, in case this is a communist plot,” Andrew said.
Example (B): “I don't know what else I can say to convince you that SRI isn't Securitate and that I'm personally not a communist.”
4) Finally, the adjective communist is not capitalized when used in conjunction with prefixes, such as pro- and anti-.
Example: “This is precisely what I didn’t want to see, two American anti-communist vigilantes interfering with an important investigation.”
I hope this helps clear up the considerable confusion with these words.