adj. Open to questioning; that which can be denied, challenged, or disputed.
the GNU version of the Collaborative International Dictionary of English
adj. Capable of being controverted; disputable; admitting of question.
The Century Dictionary and Cyclopedia
Capable of being disputed; disputable; not too evident to exclude difference of opinion: as, a controvertible point of law.
Word Usage
"By presuming that only my beliefs, practices, and perceptions are correct and unassailable implies that all others ipso facto are incorrect and controvertible."