  We define an inference system to capture explanations based on causal
statements, using an ontology in the form of an IS-A hierarchy. We first
introduce a simple logical language which makes it possible to express that a
fact causes another fact and that a fact explains another fact. We present a
set of formal inference patterns from causal statements to explanation
statements. We introduce an elementary ontology which gives greater
expressiveness to the system while staying close to propositional reasoning. We
provide an inference system that captures the patterns discussed, firstly in a
purely propositional framework, then in a datalog (limited predicate)
framework.
