SDCAR2010【逻辑入门】(八)Assumptions
An assumption is an unstated premise. In other words, an assumption is a piece of evidence that strengthens the author’s argument but that the author never sates explicitly in the stimulus.
Sufficient vs. Necessary Assumptions
Imagine that you were accused of cheating during a GMAT test. At the hearing before a panel of disciplinary committee, only one piece of evidence is presented – your one-sentence testimony: “I did not cheat at the GMAT exam.” After hearing your testimony, the panel concludes that you did not cheat. You are definitely elated. But logically, the panel’s conclusion is on shaky ground because they assume, for better or worse, that you are telling the truth! In fact there are at least three different assumptions the panel could be making.
1. You are telling the truth.
2. You told the truth at the hearing.
3. It is possible for you to tell the truth.
The first assumption that you always tell the truth is a sufficient assumption because it is sufficient or enough to justify the panel’s conclusion. If you always tell the truth, then the panel must be right. However, this assumption is not a necessary assumption or an assumption that we have to make, because the panel could still be right even if you do not always tell the truth. As long as you told the truth at your hearing, the judge is still right. In other words, the panel’s conclusion does not depend on the assumption that you always tell the truth.
The second assumption that you told the truth at your hearing is both anecessary and sufficient assumption. It is sufficient because if you told the truth at the hearing, then the panel is right; it is also necessary because if you did not tell the truth at the hearing, then the panel is wrong. In other words, the panel’s decision depends on this assumption being true.
The third assumption that it is possible for you to tell the truth is anecessary assumption because if it were not possible for you to tell the truth, then the panel would be wrong. However, this assumption is not sufficient because it alone does not justify the panel’s conclusion. Just because you can tell the truth does not mean you actually tell the truth at the hearing. Therefore, the panel could still be wrong, even if the last assumption is true.
