On the Necessary Conditions of Superposition

There are two kinds of addition,namely,superposition and accumulation.Superposition is the kind of addition that the addendums are simultaneous and at the same point and have the same property.Accumulation is the kind of addition that the addendums are not simultaneous or not at the same point.The commutative law holds for superposition without exception,but it does not necessarily for accumulation.In classic mechanics,the addendums of superposition are all about a single particle,the addition whose addendums are about different particles is not superposition unexceptionally;while the addendums of accumulation are not necessarily about a single particle.The article is very important in understanding and using the superposition principle.