"How was Don Quixote's knight-errant oath in conflict with his deathbed oath?"
Don Quixote's knight-errant oath and deathbed oath conflicted due to their complete and tremendous opposite nature. His knight-errant oath claimed that he would search out adventures, righting all wrongs, and proclaiming his love for Dulcinea. His deathbed oath claimed that he had been completely and absolutely insane in swearing the knight-errant oath.
On his deathbed, Don Quixote changed his ways, came back to sanity/reality, and denounced chivalrous books. Before this he had been living under an illegitimate oath, an oath of chivalry. This is how the two opposite oaths (knight-errant and deathbed) conflicted with one another.
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