Any contradiction or paradox.
In the thought of the German philosopher Immanuel Kant (1724–1804): an apparent contradiction between valid conclusions; a paradox.
Controversy; debate.
Struggle for superiority; combat.
A competition.
To strive earnestly to hold or maintain; to struggle to defend.
To call into question; to oppose.
To make a subject of litigation; to defend, as a suit; to dispute or resist, as a claim, by course of law.
To contend.