While most people associate logic with deductive, mathematical logic, in fact logic is a broader art. It encompassing both inductive and deductive modes of reasoning, and it applies to all of our knowledge, not just to mathematics. If one arrives at the conclusion that a ball is both solid gold and solid lead, or that Socrates is both mortal and immortal, then one has made an error. All errors in logic ultimately manifest themselves as contradictory identifications. Although the technical details may vary among fields of knowledge and among forms of reasoning, the basic rule of logic is that contradictions do not exist.
Logic begins with the evidence provided by the senses.
A process of thought based on arbitrary premises is not logic. Every logical conclusion can be traced back to and ultimate grounding in observation. See knowledge and reason for more on this issue. Return to the Objectivism home page .