Working Backwards with Copi's Inference Rules
Robert Allen · PhilPapers (PhilPapers Foundation) · 1996
In their Introduction to Logic, Copi and Cohen suggest that students construct a formal proof by "working backwards from the conclusion by looking for some statement or statements from which it can be deduced and then trying to deduce those intermediate statements from the premises. What follows is an elaboration of this suggestion. I describe an almost mechanical procedure for determining from which statement(s) the conclusion can be deduced and the rules by which the required inferences can be made. This method is designed to forestall the quandary in which many beginners find themselves: not knowing how to get started.