Expert: What criteria distinguish addictive substances from nonaddictive ones? Some have suggested that any substance that at least some habitual users can cease to use is nonaddictive. However, if this is taken to be the sole criterion of nonaddictiveness, some substances that most medical experts classify as prime examples of addictive substances would be properly deemed nonaddictive. Any adequate set of criteria for determining a substance' s addictiveness must embody the view, held by these medical experts, that a substance is addictive only if withdrawal from its habitual use causes most users extreme psychological and physiological difficulty. Which one of the following can be properly inferred from the expert's statements? ['A substance that some habitual users can cease to use with little or no psychological or physiological difficulty is addictive only if that is not true for most habitual users.', 'Fewer substances would be deemed addictive than are deemed so at present if an adequate definition of "addictive" were employed.', 'If a person experiences extreme psychological and physiological difficulty in ceasing to use a substance habitually, that substance is addictive.', '"Addiction" is a term that is impossible to define with precision.']