  According to standard liquid-state theory repulsive and attractive pair
forces play distinct roles for the physics of liquids. This paradigm is put
into perspective here by demonstrating a continuous series of pair potentials
that have virtually the same structure and dynamics, although only some of them
have attractive forces of significance. Our findings reflect the fact that the
motion of a given particle is determined by the total force on it, whereas the
quantity usually discussed in liquid-state theory is the individual pair force.
