Aristotle was both a great metaphysician and the inventor of logic, including the logic of possibility and necessity. Aristotle's Modal Logic presents a very new interpretation of Aristotle's logic by arguing that a proper understanding of the system depends on an appreciation of its connection to the metaphysics. Richard Patterson develops three striking theses in the book. First, there is a fundamental connection between Aristotle's logic of possibility and necessity and his metaphysics, a connection extending far beyond the widely recognized tie to scientific demonstration and relating to the more basic distinction between the essential and accidental properties of a subject. Second, although Aristotle's views on modal logic depend in very significant ways on his metaphysics, this does not entail any sacrifice in logical rigor. Third, once one has grasped the nature of the relationship, one can better understand certain genuine difficulties in the system of logic and also appreciate its strengths in terms of the purposes for which it was created.