Brilliant!

“In the physical universe, the addition of one stimulus is always met with the removal of another stimulus. Regardless of what type of matter (energy) this stimulus is, energy cannot be created or destroyed, and so within any given system you have to remove something to add something and you have to add something to remove something. This is a fancy way of saying that two opposing baseball teams cannot win the same game: if one team wins, the other team loses. This creates two implications: 1) that positive reinforcement and negative reinforcement (or punishment) are not mutually exclusive; and 2) if they are not mutually exclusive then you cannot stipulate that they are not occurring at the same time, let alone separately. Most examples of what dog trainers consider positive reinforcement rely significantly on negative reinforcement elements (e.g. hunger). Food is great, but as a motivator we are removing hunger (negative reinforcement), however it is also positive reinforcement for the obvious reason that we are adding food.”