A relative term for a meme that shares preconditions and conclusions with another. They are competing explanations for their connections.
A paramemetic shift is a common technique applied in the Psychochirurgical Campaign: substituting "visitors from another planet did a medical experiment on me against my will" is at least somewhat less traumatic and more comprehensible than "My psyche was altered by near-deities who do not recognize me as sentient can do it again at any time they please."