CHAPTER 3 – Inference

Publisher Summary This chapter discusses the derivability of inference. Inference is the process of deriving conclusions from premises. The ability to perform inferences of this sort is an essential part of intelligence. Inference is typically a multistep process. In some cases, one can derive a conclusion from a set of premises in a single step. In other cases, one first needs to derive intermediate conclusions. Each step in this process must be sanctioned by an acceptable rule of inference. A rule of inference consists of a set of sentence patterns called conditions, and another set of sentence patterns called conclusions. Whenever one has sentences that match the conditions of the rule, then it is acceptable to infer sentences matching the conclusions. Universal instantiation allows to reason from the general to the particular. Existential instantiation allows eliminating existential quantifiers. This rule states that one can infer an instance of the quantified sentence in which the existentially quantified variable is replaced by a suitable term.