  Armed with these distinction we may ask which properties are to be considered when we formulate the Principle. Of the various possibilities two seem to be of greatest interest. The Strong version of the Principle restricts it to pure intrinsic properties, the Weak to pure properties. If we allow impure properties the Principle will be even weaker and, I would say, trivialised. For instance in the three sphere example the impure properties being 2 units from B and being 2 units from C are possessed by A and only A, yet intuitively they do not prevent exact resemblance between A, B and C. (For a different classification of principles, see Swinburne (1995.))