  The reversibility and recurrence paradoxes are key issues that have been left
unsolved in researches on the foundation of thermodynamics since the 19th
century. This article shows that (1) the reversibility paradox can be overcome
if we pay attention to observed quantities, which represent net results of the
motion of a reversible character in the non-observable area and (2) the
recurrence paradox can be surmounted if we look at an isolated system from the
inside, in which there is no system with discrete energy levels. These
arguments confirm the validity of the reported conclusion that the origin of
the increase of entropy in an isolated system is the basic quality of
microscopic particles of spontaneously spreading into every possible spatial
area.
