第三天的课程 最重要！！Analysis of Arguments

--  作者：mike1999
--  发布时间：2003-6-10 17:35:00

--  第三天的课程 最重要！！Analysis of Arguments
第八课： Inductive and Deductive Reasoning

Many people distinguish between two basic kinds of argument: inductive and deductive. Induction is usually described as moving from the specific to the general, while deduction begins with the general and ends with the specific; arguments based on experience or observation are best expressed inductively, while arguments based on laws, rules, or other widely accepted principles are best expressed deductively. Consider the following example:      Adham: I\'ve noticed previously that every time I kick a ball up, it comes back down, so I guess this next time when I kick it up, it will come back down, too.
Rizik: That\'s Newton\'s Law. Everything that goes up must come down. And so, if you kick the ball up, it must come down.
     

Adham is using inductive reasoning, arguing from observation, while Rizik is using deductive reasoning, arguing from the law of gravity. Rizik\'s argument is clearly from the general (the law of gravity) to the specific (this kick); Adham\'s argument may be less obviously from the specific (each individual instance in which he has observed balls being kicked up and coming back down) to the general (the prediction that a similar event will result in a similar outcome in the future) because he has stated it in terms only of the next similar event--the next time he kicks the ball.

As you can see, the difference between inductive and deducative reasoning is mostly in the way the arguments are expressed. Any inductive argument can also be expressed deductively, and any deductive argument can also be expressed inductively.

Even so, it is important to recognize whether the form of an argument is inductive or deductive, because each requires different sorts of support. Adham\'s inductive argument, above, is supported by his previous observations, while Rizik\'s deductive argument is supported by his reference to the law of gravity. Thus, Adham could provide additional support by detailing those observations, without any recourse to books or theories of physics, while Rizik could provide additional support by discussing Newton\'s law, even if Rizik himself had never seen a ball kicked.

The appropriate selection of an inductive or deductive format for a specific first steps toward sound argumentation.

--------------------------------------
 
--  作者：mike1999
--  发布时间：2003-6-10 17:37:00

-- 
第九课：Introduction to Induction
As covered in the section on Inductive and Deductive Reasoning, inductive arguments are usually based on experience or observation. In effect, then, inductive arguments are all comparisons between two sets of events, ideas, or things; as a result, inductive arguments are sometimes called analogical arguments. The point of those comparisons, or analogies, is to establish whether the two sets under consideration, similar in a number of other ways, are also similar in the way of interest to the argument. Consider this example:

Mariko says, "Every time I\'ve seen a red-tinted sunset, the next day\'s weather has been beautiful. Today had a red-tinted sunset, so tomorrow will be beautiful."
Essentially, Mariko is comparing one set of events (observed red-tinted sunsets and each following day\'s weather) with another (today\'s observed sunset and tomorrow\'s predicted weather). These sets are similar in an important way (red-tinted sunsets), and the inductive argument is that they will also be similar in another way (nice weather on the following day). In this case, Mariko is arguing from particular cases in the past to a particular case in the present and future, but she could also argue inductively from those particular cases to a general one, such as "It\'s always beautiful the day after a red-tinted sunset."

The strength of such an argument depends in large part on three of its elements:

how accurate and comprehensive the previous observations are;
how strong the causal link seems to be;
how similar the two cases are.
In Mariko\'s argument, to satisfy the first element, we would want to be sure that she\'s seen many such sunsets, and that "redness" and "beauty" have been judged consistently. To satisfy the second, we would want to feel confident that there is a strong correlation between weather patterns on successive days. To satisfy the third, we would want to know whether there are any significant differences between the observation of today\'s sunset and of the previous ones. A difference in season, a difference in geographical or topographical location, a difference in climate, or any other significant variation might affect the comparability of the two sets of observations.

In fact, we should always understand the second premise of an inductive argument to contain a claim like "there is otherwise no significant difference." The second premise of Mariko\'s argument, then, might read, "Today\'s sunset was red-tinted (and there were no significant differences between this and previous red-tinted sunsets)." Keeping such a disclaimer in mind is important, because this is where many inductive arguments are weakest.

Because we argue inductively from the particular to the general, such arguments are often called generalizations, or inductive generalizations. Other kinds of arguments with a similar format include causal arguments.

--------------------------------------
 
--  作者：mike1999
--  发布时间：2003-6-10 17:38:00

-- 
第十课：Introduction to Causal Arguments
One of the most important uses for inductive reasoning is to argue causation. Consider the following example:

A bicyclist moves into the traffic lane in order to pass a truck illegally parked in the bike lane. The driver of a car approaching from the rear slams on her brakes in order to avoid hitting the bicycle. A following car fails to stop in time, and smashes into the back of the first. The insurance companies disagree about who should be held responsible, and they go to court to decide who caused the accident.

What arguments are likely to be made in court? The bicyclist\'s lawyer will probably claim that the illegally parked truck caused her client to swerve into the lane of traffic. The lawyer for the driver of the first car will probably claim that the bicyclist\'s actions caused her client to slam on the brakes. The lawyer for the second driver will probably claim that the first car\'s sudden stop caused his client to smash into its back.

None of these claims seems to fit the pattern of an inductive argument, because none of them seems based on observation or experience. But, in fact, they do fit that pattern. The bicyclist\'s lawyer, for example, is actually arguing that:

Normally the bicyclist would have continued in the bike lane, but in this instance he swerved into the lane of traffic.
The only signficant difference between "normally" and "in this case" is the presence of the illegally parked truck.
Therefore, the truck caused the bicyclist to swerve.
The lawyers for the drivers are making similar arguments: the first, that the only signficant difference was the swerving bicycle; and the second, that the only signficant difference was the suddenly braking car. Like inductive reasoning, then, these causal arguments are based on observed instances. (In this case, no observations are needed to convince us that the bicyclist would not normally have swerved or the first driver would not normally have braked suddenly. But if, for some reason, observations were necessary, we could design a study of automobile and bicycle traffic on that street, or survey drivers and bicyclists about their experiences, or in other ways provide evidence to verify the part of the premise describing the normal pattern of traffic. For more on this, see the section on Studies, Surveys, Polls, and Experiments.

These causal arguments, then, follow the form of an inductive argument with one important exception: whereas an inductive argument carries as part of its second premise the implication that there is otherwise no significant difference, these causal arguments carry the implication that there is only one significant difference: for the bicyclist, the truck; for the first driver, the bicycle; for the second driver, the first car.

How can we know that there is really only one significant difference? In real-life situations, we cannot usually be certain of that, since the world in which we live is a very complicated and intricate place. If, however, there is a strong likelihood of causation and there are no other apparent causes in evidence, then the argument will seem convincing. Two rules to remember in dealing with causation are:

The cause must precede the event in time. On one hand, arguments that have the effect before the cause are examples of the relatively rare fallacy of reverse causation. One the other, arguments whose only proof of causation is that the effect followed the cause are examples of fallacious post hoc reasoning.
Even a strong correlation is insufficient to prove causation. Other possible explanations for such a strong correlation include coincidence, reversed causation, and missing something that is the cause of both the original "cause" and and its purported "effect."
In the trial, for example, the second driver\'s lawyer could not argue that his client hit the first car because the first car stopped suddenly if reverse causation, post hoc reasoning, or a common cause is found. An example of reverse causation would be that the accident occurred before the first car began to stop, and it only came to a sudden stop because it was hit. An example of post hoc reasoning would be that the only connection between the stopping and the accident is that the car stopped first (say, Tuesday), and the accident happened later (say, Thursday). An example of a common cause would be that the reason the first car stopped suddenly and the reason that the second car hit it are the same: they were both side-swiped by a large recreational vehicle.
But what if, as the trial progresses, evidence is introduced to show that the bicyclist has a history of causing accidents by swerving in front of cars, or that the first driver has been involved in several accidents in which she caused her brakes to lock, or that the second driver was speeding and the street was slick? Such information could lead to very different causal arguments, where the implied claim does not concern "the only signficant difference," but rather "the only significant commonality." The bicyclist\'s lawyer might argue, for example, that her client\'s swerving may have caused the first driver to brake suddenly, but that the accident was caused by the way in which the first driver hit the brakes, and that she has caused similar accidents that way in the past. The first driver\'s lawyer, on the other hand, might argue that the accident was caused not by her client\'s braking, but by the second driver\'s unsafe speed, and the slick condition of the road, and that these factors have often caused other accidents. Both lawyers would be using a causal argument based on "the only signficant commonality."

Often, complex causal arguments use a mixture of "difference" and "commonality" reasoning, to show that the proposed cause is the only significant difference in cases where the effect did not occur, and the only significant commonality in cases where the effect did occur.

The strength of a causal argument, then, relies on three factors:

how acceptable or demonstrable the implied comparison is (for example, do we think that there is a basic similarlity in most respects between the circumstances of this accident and those of the many other times bicycles and cars have traveled on this street safely;
how likely the case for causation seems to be (for example, do we think that a bicycle swerving into an car\'s lane can cause an accident?);
how credible the "only significant difference" or "only significant commonality" claim is (for example, do we believe that the illegally parked truck is the only significant difference between this case and the many other times bicycles and cars went down that street without an accident?).
--------------------------------------
 
--  作者：mike1999
--  发布时间：2003-6-10 17:41:00

-- 
argument可以分为deduction and induction两种，今天介绍的是inductive arguments.明天向大家介绍Deductive Arguments，其中包括：Conditional Arguments，
"Only" in Conditional Arguments，Conditional Chain Arguments，Universal Syllogisms
和Non-Universal Syllogisms。
--------------------------------------
 
--  作者：albert
--  发布时间：2003-6-10 20:29:00

-- 
great job! mike, thanks!

--------------------------------------
原文引自：
https://forum.chasedream.com/dispbbs.asp?boardid=24&id=6106

参与签证讨论及查看讨论及查看更多的相关文章请访问【GMAT逻辑专区】
https://forum.chasedream.com/list.asp?boardid=24