Practical reasoning is a goal-directed sequence of linked practical inferencesthat seeks out a prudent line of conduct for an agent in a set of particular circumstances known by the agent. Where a is an agent, A is an action, and G a goal, thetwo basic types of practical inferences are respectively, the necessary conditionscheme and the sufficient condition scheme (Walton, Pract. Reas., 1 990; see alsoSchellens, 1 987).G is a goal for aDoing A is necessary for a to carry out GTherefore, a ought to do AG is a goal for aDoing A is sufficient for a to carry out GTherefore, a ought to do A