Therefore, everyone who smokes marijuana becomes hopelessly addicted to it. When a cook can't recall the ingredients in a recipe, it is appropriate that he or she refresh his or her memory by consulting the recipe book. Similarly, when a student can't recall the answers during a final exam, it is appropriate that he or she refresh her memory by consulting the textbook. No dogs are creatures that live for more than 30 years. All municipalities that have a very good city planners are places in which it is desireable to live.
All oil spills are events catastropic to the environment.
Some corporate lawyers are not persons with a social conscience. No alcoholics are persons with a healthy diet. Some tax proposals that favor the rich are not fair proposals. If you fail to produce a proof of an immediate inference, then you are entitled to conclude that the argument is invalid. If the premise of an argument is logically equivalent to the conclusion, then the argument is valid.