Fifth, class systems vary with respect to the degree of mobility which is possible within them.  In some, as in the case of sexual and racial class systems, the positions of individuals are virtually fixed.  In others, movement is possible in widely varying degrees (1966, p.82).

Sixth, class systems differ in terms of the degree of hostility which prevails between classes.  In a few instances, class warfare of the type envisioned by Marx has prevailed, at least for a time.  At the other extreme, there has often been a virtual absence of hostility.  There is good reason for supposing that class hostility is inversely related to opportunities for mobility, though available evidence suggests that the relationship is far from perfect (1966, p.82).