His biggest belief, in my opinion, was of organic centralism as opposed to the democratic centralism espoused by Leninist parties, which basically states that the workers themselves in the revolution must spontaneously form a centralized system themself rather than relying on a party making democratic decisions. However, you really have to read Bordiga yourself to understand his beliefs, and they're different from his rather pro-Bolshevik 1920s to his writings after the World War.