This book presents a realist theory of causal metaphysics founded on a detailed ontological treatment of dispositional properties, or powers.
The book is a posthumous publication, Molnar having died in 1999. Some interesting biographical information is provided in the introduction by Stephen Mumford, as well as in a preface by D. M. Armstrong. Mumford also prepared the manuscript.
Molnar's theory is a realist account of dispositional properties as causal powers. This realism about dispositional properties and causality is in contrast to work in the Humean tradition which would eliminate dispositional properties and reduce apparent causal power to mere correlation. A traditional strategy is to employ a conditional analysis. Rather than ascribe the dispositional property of solubility to X, one simply notes that if X is placed in water, then it will dissolve. Another way to approach eliminating powers is to claim they can be reduced to categorical micro-physical properties (although many would view charge, mass, spin et. al as paradigm dispositional properties). Molnar defends dispositional properties as real and ineliminable causal powers of objects. He sees these as ubiquitous features of our world.
It is an impressive and interesting effort. In my opinion we need a theory of "real" causation, and this is a well-argued candidate theory. In the end, I disagree with the theory, but my thinking on the topic of causation was greatly enlightened and sharpened by Molnar's work.