Imagine that you and I are hiking up a path to a mountaintop. There is a rumble and a minor earthquake dislodges a boulder that now blocks the way forward. Together we come up with a way to negotiate the obstacle.
Finding a way around, over or through an obstacle is a definition of negotiation in which the adversary is the obstacle.
We fight in wars, battles and conflicts. We negotiate truce, overcoming the obstacles of war.
It is not unusual to witness parties in mediation approach conflict as war, determined to win. It takes two to tango and at least two for conflict to exist. Defining negotiation as an obstacle to collectively overcome is a practical way to turn conflict into disagreement and work together toward resolution.