Philosophy 105
Fall 2005
Lecture Notes - Chapter 6
Once you have figured out the main point of an argumentative passage it is relatively easy to come up with a rough statement of the argument. What’s often hard is getting the reconstruction into proper form. This chapter reviews some of the main problems that arise at this stage of analysis and suggests some things to correct them. There are three general ideas: i) tighten up wording so that you are using standard patterns, ii) state justifications, iii) omit unnecessary premises. All of these enable you to fine-tune your reconstructions.
One way to proceed is to write down all the sentences from a short argumentative passage, identify one as the conclusion, and then consider all the rest as potential premises. With practice, you will be able to eliminate some of the potential premises, restate others in better ways, and add the required implicit premises. Some illustrations of the method follow.
A. p. 159, #15: (1)-(5) are EPs, (6) follows from (1) and (5), (7) from (2) and (4), and (8) from (3), (6), and (7).
B. p. 164, #4-7: (4) - omit (1)-(3). Or, add a generalization such as: all things that will lead to the president’s not being reelected are things the president will try to prevent.
(5): Omit (3).
(6): Omit (1). (Also, could replace (3) by a disjunction - either you will or you won’t.)
(7): Omit (7). (Also, could revise (1).)
C. Exercise 9, p. 166.
“Students who come to school under the influence of drugs are disruptive and interfere with the education of other students. Students have a right to a quality education and the school board must not permit some students to interfere with the education of others. So we should test students to see if they are using drugs. Drug users should not be permitted to attend school.”
a) What’s the main conclusion?
Here are first versions of two possibilities:
C1. Students should be tested for drugs.
C2. Students who use drugs should not be permitted to attend school.
It’s somewhat hard to tell without going through the rest of the passage, but the point of the argument seems to be (C1). It may be that (C2) is part of what’s needed to support (C1).
Note: missing quantifiers in both statements. Background info. and the context of the discussion suggest that the intended conclusions are universal generalizations.
b) What are the explicit premises?
Here are some possibilities:
1. Students who come to school under the influence of drugs are disruptive and interfere with the
education of others.
2. Students have a right to a quality education.
3. Students should not be permitted to interfere with the education of others.
c) What implicit premises, if any, are needed to make the argument well-formed?
A first reconstruction looks like this:
1. Students who come to school under the influence of drugs are disruptive and interfere
with the education of others. [EP]
2. Students have a right to a quality education. [EP]
3. Students should not be permitted to interfere with the education of other students. [EP]
4. So, drug users should not be permitted to attend school. (1) - (3)
5. If (3) is true, then students should be tested to see if they use drugs. [IP]
6. Students should be tested for drug use. (4), (5)
d) Fine-tune your reconstruction:
a) Missing quantifiers in several steps.
b) (5) is insufficiently general.
c) Wording needs to be tightened up in a few places. Eg., (1) and (3) don’t match.
d) (2) isn’t really needed. (Or maybe it supports (3).)
e) (4) does not follow from (1) - (3).
f) There’s a question about what quantifier to use “all” or “some” at various places in this argument. One possibility is to use “all” throughout. And we can combine (2) and (3) into one premise that will get us to (4) in the original version:
1. All students who come to school under the influence of drugs interfere with the
education of others. [EP]
2. All students who interfere with the education of others should not be allowed to attend
school. [EP?]
3. All students who come to school under the influence of drugs should not be permitted
to attend school. (1), (2)
4. If all students who come to school under the influence of drugs should not be permitted
to attend school, then all students should be tested to see if they are under the influence of
drugs.[IP]
5. All students should be tested to see if they come to school under the influence of drugs.
(3), (4)
We still haven’t made (4) general. More on this later. (1) is plainly false.
We could make (1) true by changing the quantifier to “some”. But then this part of the argument is
1. Some students who come to school under the influence of drugs interfere with the education of
others. [EP]
2. All students who interfere with the education of others should not be allowed to attend school. [EP?]
3. All students who come to school under the influence of drugs should not be permitted to
attend school. (1), (2)
This is ill-formed.
Replace ‘all’ in (3) by ‘some’. Now we have:
1a. Some Ds are Is.
2a. All Is are Ps
3a. Some Ds are Ps.
[D= students who come to school under the influence of drugs; I=interfere with the education of
other. P=students who should not be permitted to attend school]
This part is now valid. (1) is true. (2), perhaps, is true. At least, it expresses the intended idea.
But now consider the second part of the argument. How do we get from (3a) to the conclusion? Suppose we continue with (4) and (5) from above.
3a. Some students who come to school under the influence of drugs should not be
permitted to attend school. (1), (2)
4. If all students who come to school under the influence of drugs should not be permitted
to attend school, then all students should be tested to see if they are under the influence of
drugs.[IP]
5. All students should be tested to see if they come to school under the influence of drugs.
(3), (4)
This is invalid.
Replace both occurrences of ‘all’ in (4) by ‘some’. Also make the change in (5). Now we have:
3a. Some students who come to school under the influence of drugs should not be
permitted to attend school. (1), (2)
4a. If some students who come to school under the influence of drugs should not be
permitted to attend school, then some students should be tested to see if they are under
the influence of drugs.[IP]
5a. Some students should be tested to see if they come to school under the influence of
drugs. (3a), (4a)
Valid. But notice that this makes the argument not have the conclusion some thought it should have. It’s not now an argument for universal testing, which was precisely its point.
You could replace the “some” in the consequent of (4a) with “all” and also do the same in the conclusion, thus reinstating the original conclusion. Symoblizing:
1a. Some Ds are Is. [EP]
2a. All Is are Ps [EP?]
3a. Some Ds are Ps. (1)-(3)
4. If (3), then all students should be tested for drugs. [IP]
5. All students should be tested for drugs. (3), (4)
Now, finally, we have a valid argument for the intended conclusion. (1a) is true. (2a) is at least somewhat plausible, and it does capture the idea advocates of this view probably hold. One could debate whether expulsion is really the best way to deal with the disruptive students. And (4) does capture their idea as well: if some people with a certain property cause a problem, then test everyone for that property.
But there’s a question about (4). It’s the same as the question about (2) above. The generalization of (4) is something like this:
If some people who have a certain property should not be permitted to attend school, then everyone should be tested to see if they have that property.
Is this plausible? Perhaps a comparison to airport security would be instructive. You might think that a similar argument for checking all travelers would be comparable. But, you might also think that the argument for checking people before they get on a plane is a good one, so this one is as well. A key idea is brought out in this proposed reconstruction:
1. All students who take drugs are at an unacceptably high risk of becoming disruptive and interfering with the education of other students. [IP?]
2. All students who are at an unacceptably high risk of becoming disruptive and interfering with the education of other students should not be allowed to attend school. [IP]
3. All students who take drugs should not be allowed to attend school. (1), (2)
4. If (3), then the best method for identifying which students take illegal drugs should be implemented. [IP]
5. The best method for identifying which students take illegal drugs should be implemented. (3), (4)
6. Universal drug testing is the best method for identifying [IP]
7. So, universal drug testing should be implemented. (5), (6)
(1) brings in the idea of risk. That’s a good thing to do here - people with guns on planes cause a serious risk. And maybe the idea is that students on drugs are like that. (1) says that they do. (1) brings out a key idea that helps us to think about what’s really at issue here. In the airport screening case, the risk of not checking is so great that it’s worth doing. If there’s a good argument for drug testing there, it is similar. It can help to break the argument up into two parts, like this:
Argument A
1. All students who take illegal drugs pose an unacceptably high risk of becoming disruptive and interfering with the education of others. [IP?]
2. All students who pose an unacceptably high risk ... should be kept out of school. [EP?]
3. So, all students who take illegal drugs should be kept out of school. (1), (2)
Argument B
1. All students who take illegal drugs should be kept out of school. [From Arg. A]
2. If (1), then the best method for identifying which students take illegal drugs should be implemented. [IP]
3. The best method for identifying ... (1), (2)
4. Universal drug testing is the best method for identifying [IP]
5. So, universal drug testing should be implemented. (3), (4)
The logical structure here is pretty hard, and I won’t try to display it. This is valid (there are complications in Arg. B, but it’s ok). We will not go into the evaluation of this now. But you can think about the merits of Arg. A. Is the risk that great? Compare
1. All people carrying guns pose an unacceptably high risk of harming other passengers on airplanes.
2. All people who pose an unacceptably high risk... should be kept off planes.
3. So, all people carrying guns should be kept off planes.
This seems ok. But you might think that the risk in the airplane case better warrants keeping them out than does the risk in the drugs in school case.
Notice how far we have come from the original. It’s hard to say that this is what the author had in mind. But it is a reasonable argument to consider in light of what he wrote.