Given the velocity field of a continuous-time homogeneous Markov system (HMS) with fixed size, it is examined if the system could be considered as a continuum. The model examined is that of a Newtonian fluid. The set of attainable structures is the continuum and its evolution in Euclidean space corresponds to the motion of the continuum. It is proved that the Newtonian fluid assumption cannot generally explain the motion of the HMS. If it is possible, then we come to the conclusion that the ‘viscosity’ is a function of density and position. The dependence of viscosity on position implies that a fluid conforming to the HMS cannot be real. © 1998 John Wiley & Sons, Ltd.