“and “particular individual agreed with another, to rumble” is what has to exist in order to find conspiracy.”
Actually not. Associating for the cause of criminal activities establishes a conspiracy. If one of the associating commits a crime for the furtherance of the association, then others may also be charged even if they had not conspired to that specific crime.
You assume the conclusion there. Your statement is a truism, "if they conspired, that establishes a conspiracy." Association with nothing more does not establish conspiracy.
-- If one of the associating commits a crime for the furtherance of the association, then others may also be charged even if they had not conspired to that specific crime. --
True in the abstract, but a legally sufficient accusation against the others requires more than an association with the criminal actor.