Nonclarity around the understandingof the concept of chaos has caused someconfusion in the contemporary natural science.For instance, not making a clear distinctionbetween the deterministic and quantum chaos hasmade it impossible to evaluate the approach ofIlya Prigogine in an appropriate way. It isshown that Jean Bricmont has missed the targetin his critique of I. Prigogine's ideas, as thelatter has concentrated his interest on systemsconsisting of infinite (arbitrarily large)number of particles in incessant mutualimpact, the former on systems that have afinite (not necessarily large, althoughsometimes very large) number of particles,which move freely of any mutual impact orparticipate only in transient interaction. Thedifference may sometimes be quite crucial. Itis also suggested that if we consider theirreversibility as the basic element ofdescription of physical world, the world oftrajectories and wave functions cannot beresearched apart from this real irreversibility.