Compoundation Invariance and Bohmian Mechanics

The property of fundamental mechanical theories which allows to treat compound objects as particles under suitable conditions is considered. It is argued that such a property, called compoundation invariance, is a nonreleasable property of any mechanical theory not declaring to which elementary constituents it applies. Compoundation invariance is discussed in the framework of Bohmian mechanics. It is found that standard Bohmian mechanics satisfies the requirement of compoundation invariance, with some reservation in the case of compound objects with spin. On the contrary that requirement is violated when additional terms are added to the standard velocity.