The stimulus argues against a certain definition of "addiction" as "dependence on and abuse of a psychoactive substance." The main premise is that dependence and abuse are not always linked, and the argument appeals to two examples to demonstrate this point: cancer patients dependent on morphine to reduce pain, but not abusing it, and people abusing a drug without being dependent on it. The argument concludes that the definition cited for addiction is incorrect.

This argument rests on a number of assumptions. Notice that just showing that two phenomena, A and B (in this case, dependence and abuse), don't always occur together, doesn't mean that when they do occur together, they don't constitute a unique third phenomenon, C (in this case, addiction). To defeat the definition of C as "A AND B," the argument assumes that the cases of only A and only B also qualify as phenomenon C.

Let's use an analogy. Imagine a rule: "to get into the concert, you need both a ticket and a wristband." If I respond by saying, "That can't be true! That person over there has a wristband, but no ticket. And that person over there has a ticket, but no wristband." You can probably see that the effectiveness of my argument completely depends on whether those people got into the concert or not. If they didn't get into the concert, then these examples are completely irrelevant: it doesn't matter that A and B (wristband and ticket) can occur independently; you still need both for phenomenon C (getting into the concert). But if those people did get into the concert, then I have effectively undermined the rule.

In the same way, the question about the cancer patients dependent on morphine and the people abusing the drug without being dependent on it is: do these cases qualify as addiction? If not, then they aren't relevant to the definition at all, and the argument falls apart. If so, then they show that the definition, by requiring both dependence and abuse to qualify as "addiction," is too restrictive.