Suffixes:
* -ity: Creates a noun meaning "the state or quality of being rational."
* Rationality: The ability to think clearly and logically.
* -ize: Forms a verb meaning "to make rational."
* Rationalize: To find a logical reason for something, even if it's not the real reason.
* -ly: Forms an adverb meaning "in a rational manner."
* rationally: To think or act in a logical and sensible way.
Prefixes:
* ir-: Creates the opposite of "rational," meaning "not rational."
* irrational: Lacking logic or reason; illogical.
* un-: Also creates the opposite, emphasizing the absence of rationality.
* unrational: This is less common, but could be used to emphasize the complete lack of rationality.
* over-: Can create a sense of excessive rationality, leading to a negative outcome.
* over-rationalize: To excessively explain something with logic, potentially ignoring other important factors.
Other:
* -ism: Can be added to create a noun meaning "a theory or system based on rationality."
* Rationalism: A philosophical doctrine that emphasizes reason and logic as the primary sources of knowledge.
It's important to note that not all combinations will be commonly used. Some may sound awkward or have unusual meanings.
Remember: The best prefix or suffix to use depends on the specific meaning you want to convey.