 It is important to appreciate, however, that establishing the existence of atoms in this way left many of the questions raised by the skeptics unanswered. A theory of the nature of atoms which would explain how they can combine to form molecules was yet to be formulated. And it remains to this day an open question whether a purely microscopic theory is available which is adequate to explain the whole range of chemical phenomena. This issue is pursued in Section 6 where we discuss reduction.