There is a common mistake in thinking that if a fact is wrong, the logic must be broken. However, deductive reasoning shows us that an argument's validity is entirely about its formal structure, independent of whether the premises are actually true.

This discussion moves away from scientific observation to explore the purely rational world of deductive logic. We examine how arguments are constructed using premises and conclusions, and why validity acts as a truth-preservative. By understanding the different types of propositions—from categorical class relationships to complex biconditional statements—we gain the tools to evaluate the consistency of any rational claim.

• The definition of validity as a logical impossibility for true premises to lead to a false conclusion.
• How a valid argument can still lead to a true conclus ...