Formal logic helps us build and evaluate rational arguments, which helps us to test claims, explain our reasoning, and keep discussions clear. The first step in learning formal logic is learning about deductive arguments -what they are, how they are structured, and how they can go wrong. The Parts of a Deductive Argument Deductive arguments are built out of premises and conclusions. For example, here is a simple deductive argument: The first two sentences are the premises. The last sentence is the conclusion. Premises are statements that support the conclusion.