GMAT考试写作指导：Argument范文六八

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22.        The conclusion in this argument is that increased vigilance by drug enforcement
authorities has resulted in an increase in the illegal use of cocaine. The author reaches
2 B$ m0 m. B4 X8 Qthis conclusion on the grounds that drug traffickers have responded to increased
$ `1 Z3 w4 K9 }/ `1 Y5 X0 h! ]( `* {1 q" @enforcement efforts by switching from bulkier and riskier drugs to cocaine. Presumably,
the author's reasoning is that the increased enforcement efforts inadvertently brought
1 m7 u( S4 D) v% _( e) r6 Eabout an increase in the supply of cocaine which, in turn, brought about the observed
increase in the illegal use of cocaine. This line of reasoning is problematic in two
+ R% k! q3 _3 v/ R) uimportant respects.
      In the first place, the author has engaged in "after this, therefore because of this"
reasoning. The only reason offered for believing that the increased vigilance caused the
# G$ G% K7 p+ Z6 V2 bincrease in cocaine use is the fact that the former preceded the latter. No additional
evidence linking the two events is offered in the argument, thus leaving open the
1 A$ }) i3 D' H6 fpossibility that the two events are not causally related but merely correlated. This in turn
leaves open the possibility that factors other than the one cited are responsible for the
! k" f! R4 A5 ]increase in cocaine use.
      In the second place, the author assumes that an increase in the supply of cocaine is
8 D: E/ j* P7 l1 Ssufficient to bring about an increase in its use. While this is a tempting assumption, it is
& T; o) Z" @3 d+ k& C- ia problematic one. The presumption required to substantiate this view is that drug users
are not particular about which drugs they use, so that if marijuana and heroin are not
& ?+ e& Z, d* e- j4 b8 l* Oavailable, they will switch to whatever drug is available—cocaine in this case. The
assumption does not seem reasonable on its face. Marijuana, heroin, and cocaine are not
/ v# k* T4 B) |6 _: ~7 w$ Jalike in their effects on users; nor are they alike in the manner in which they are
ingested or in their addictive properties. The view that drug users' choice of drugs is
+ M# e8 o, r9 Q- c1 e; v8 fsimply a function of supply overlooks these important differences.
0 y5 d+ e. ]0 }  H* c& _      In conclusion, the author has failed to establish a causal link between increased
# l) s. K5 O8 Jenforcement efforts and the observed increase in illegal cocaine use. While the
& C" d% e8 I3 g6 ]' I1 kenforcement activities may have been a contributing factor, to show a clear causal
9 M4 K; s: L3 X7 C+ S# Iconnection the author must examine and rule out various other factors.