Critical Thinking Core Concepts

by: Lauren Miller and Michael Connelly, Longview Community College

Short history of Logic

If we take Logic to be the activity of drawing inferences (conclusions) from a body of information, then no doubt humans have been using logic for as long as they have been thinking, or at least consciously thinking. The first Neanderthal to formulate the thought "All members of the Cave-Bear clan are our enemies" along with "Thag is a member of the Cave-Bear clan" very likely put the 2 and the 2 together and reached the conclusion "Thag is our enemy". Nor is there any particular reason to suppose that the logic of these primitives was primitive logic-- that is, they probably drew logically correct conclusions from their data about as often as folks do nowadays (i.e. maybe 62.3% of the time). (Besides, chances are that natural selection quickly weeded out the Neanderthals who tended to draw the conclusion "Thag is our friend" from the above data!)

On the other hand, if we take Logic to be the analysis of concepts involved in making inferences, and the identification of standards and patterns of correct inference, Logic can be traced only back to the days of Aristotle (350 years B.C. or so), with some parallel development in early Hindu writings. It's not clear that this increase in logical self-consciousness improved the accuracy of reasoning processes for humankind in general, but knowing what Aristotle knew about logic can definitely help you be a better reasoner.

Around the end of the 19th century, Logic received renewed interest (and an emphasis on symbolic representation), from mathematicians in search of a fundamental connection between logical and mathematical reasoning. Development of, and reaction to, this line of inquiry led to two divergent lines of emphasis in the study of logic, which you may have heard of:

Symbolic (or Formal) Logic vs Informal Logic (or Critical Thinking).

In a typical symbolic logic course, emphasis is placed on the precise symbolic representation of logical concepts, the study of the abstract relationships between these concepts, and the systematization of these relationships.

In an "informal logic" or Critical Thinking course, such as ours here at Longview, the focus is instead on the application of logical concepts to the analysis of everyday reasoning and problem-solving. Elements of symbolic logic will frequently be involved, but only to the extent that it contributes to this practical objective.

Notice that neither of these directions of emphasis really concern themselves much with how people actually think, or what you might call a psychology of thought. Informal Logic begins with the perception that people don't actually reason all that well, but jumps from there to the matter of doing something about it. Symbolic Logic begins with the perception of what constitutes good reasoning at a rudimentary level, and goes on from there to investigate good reasoning at higher and higher levels of sophistication.

What is the point of studying Critical Thinking?

Introducing logical vocabulary

Statements or propositions

A statement is a sentence which "has a truth-value" - i.e., one which is either true or false. Your English teacher will refer to these as declarative sentences, which they are called for the obvious reason that they are good for declaring that things are so or not so. What you declare to be so may really be so, in which case the "truth value" of the statement will be T (for True). Or it may not really be so, in which case the truth value of your statement is F (for False).

The truth value of a given statement may be unknown, but that doesn't keep us from telling that it HAS a truth value. For example, you don't know, and neither do we, whether the statement "There is a 10.756 kilogram rock on the dark side of the moon" is true or false, but we all know that either there is such a rock (in which case the statement has truth-value T) or there's not (and the truth-value would be F).

When you really get sophisticated you can do like the big guys do and bring in truth-values like M (for maybe) or U (for Unknown) or S (for Sorta). But for now, do we need to make it any more complicated?

Some types of sentences which are NOT statements are:

Statement is an easy and straight-forward concept. Where things get a tad tricky is when it comes to making, or expressing statements. The obvious, practical, and straight-forward way of expressing a statement is just to say it. Someone who says, "The moon is 150 miles above the earth," is expressing the statement: Someone taking the opposite view of the matter could just say,"The moon is not 150 miles above the earth," which expresses very well the statement Probably, though, that won't be what they'll say, since it's so obvious, practical, straightforward, and boring. They'll say, All of these responses, in this context, express the statement Statements are one thing, how people go about expressing them is another. In determining what viewpoint a person is taking, or what they are saying in defense of that viewpoint, one of the fundamental steps is to determine what statements their actual words express. There are no rules for this basic translation process. You just have to rely on what you know about the language, and the speech customs of its speakers.

Peddlers and Consumers of Statements
In real life, people sometimes make statements just to be speaking the truth. But frequently they make statements, not primarily (and maybe not even secondarily) to be speaking the truth, but primarily in order to get other people to accept them as true. Then we call this peddling the statement, and we call the those who peddle it the peddlers of it, and those whom they want to accept it the consumers of the statement. The context of this human interaction is called a "context of persuasion", or sometimes "the propositional marketplace" (since there's no such word as "statemental".)

Being a skilled critical thinker will require, in the long run, knowing a lot about the propositional marketplace and the various devices a peddler may use (deliberately or not), which ease the consumer into accepting the statement being peddled. For now, just remember this key feature of the propositional marketplace: somebody (the peddler) wants somebody else (the consumer) to believe something (a statement).

Note that we are not necessarily speaking here of professional roles. You are a peddler every time you say something with the purpose of getting someone else to believe it- regardless of whether you're paid to do this or not (in other words, usually not). Likewise, you are a consumer every time you are the target audience of someone's peddling attempt. So most normal people alternate between these functions many times every day.

Interestingly, you can even peddle statements to yourself, in the privacy of your own mind. Down there in that internal forum (in foro interno), with no outsiders paying attention to the process, you very rarely think just one isolated thing. Have you ever noticed that? You think- or notice, or pay attention to- one thing, and then on the basis of that you think some additional thing. For example, you might think "I've got a logic exam this Friday!", and right away one or more additional thoughts attach themselves, like

That's you the peddler talking. You the consumer usually just sits there and accepts these additional thoughts without critique or resistance. But your internal peddler is capable of being just as crafty as any external peddler may be. So if it's your internal consumer who's in charge of investing your life energies into some picture of the truth, then that consumer had better pay the same close attention to this internal process of persuasion as to an external one.

The sign of a top-notch, first-class critical thinker is this tendency to apply to persuasion processes in foro interno the same standards and attitudes that are appropriate to ones in the external forum.

Things Peddlers Do

What a peddler does in order to gain acceptance for his (or her) statements can include all sorts of crazy things:

All of these techniques are effective to some degree - some more with some people than with others, some more in one context than in others. Some rely for their effectiveness on good qualities in the consumer (like sympathy, or trust); some rely on bad qualities (like fear, or ignorance). But exactly none of them have anything to do with the truth of the statement being peddled - they'd work just as well with lies as with the truth.

So here's the big question: is there anything a peddler could provide that would show the consumer that the statement being peddled is true? Then the consumer could accept it because she sees that it's true, and just disregard all the accompanying song-and-dance.

The answer to that question is yes, with certain qualifications:

Political and Philosophical Peddlers
You are fortunate if you encounter a peddler who is interested in getting you to agree with a statement by showing you that it is true. We refer to such peddlers as philosophical, because of their orientation toward the truth (philosophical means "loving wisdom"). Peddlers who just want to get you to agree, regardless of truth, we refer to as political, since power and control are their main concerns.

So we see that a philosophical peddler will try to point out to you facts that you already accept as true, and show you that in view of these the peddled statement is true (or at least probably true). When you consider that facts are expressed by statements, you see that this peddler's essential pitch consists of a collection of statements:

So, to summarize: Beyond Simple Statements, we will also have to consider compound statements; will be of four main types, which correspond to the four main types of logical connectives-

1. Conjunctions- (A and B) - for statement to be true both A and B must be true, if either of them is false, statement is false.

2. Disjunctions- (A or B) - for statement to be true only one of the component simple statements need be true.

3. Negations- (NOT A) - in this type of statement the simple statement is modified so that the truth value is reversed.

4. Conditionals- (IF A, THEN B) - in this statement, the first part is identified as the antecedent, and the second part as the consequent. For this statement to be true, the condition expressed for the truth of B must not be compromised. The only case when this happens is when A is true and Bis false.

It is possible to represent the truth values of each of these statements with what is called a 'truth table'. Each kind of statement will have its own truth table which will represent all of the possible combinations of truth and falsity for the simple statements and the resulting truth or falsity of the compound statement of which they are a part.

Arguments:

Such a collection of statements is called an ARGUMENT. The supporting statements are referred to as PREMISES, and the one supposedly being supported is called the CONCLUSION. In presenting an argument, the peddler is not just stating a list of separate facts, but rather is seeking to JUSTIFY (show the truth of) one statement by offering the other statements as support for it.

Note that these are technical terms. An argument is a collection of statements, not "a squabble". The premises are the statements given in truth-support for the conclusion-- not to be confused with the "physical location" of anything. The conclusion is the statement which is being given truth-support by the premises, which is not necessarily "the last thing said".

Based on this concept of an argument, and an understanding of its use in contexts of persuasion, we can form a broad outline of the main phases of CRITICAL THINKING:

RECONSTRUCTION- deals with extracting an argument from the surrounding mix of statements which a peddler may have presented.

ASSESSMENT- deals with the business of determining whether the structure of an argument really would permit truth to be carried from the premises to the conclusion.

EVALUATION- deals with the activity of judging whether the premises of an argument are true or false, clear or vague, and in need of further defense or not.

FALLACY IDENTIFICATION- deals with the multifarious list of things that may happen in a persuasion context, leading to the consumers' accepting some statement without adequate justification.

We should note here that in addition to this critical thinking approach, there are other perspectives from which a given presentation could be analyzed. We could look at the rhetorical power of the presentation - focusing on its emotional content, or on the style with which it was presented, and the impact these things have on the receiving audience. Or we could concentrate on its literary merit - focusing on the novelty or creativity of the argument, among other things. These two are the aspects which are usually concentrated on by the media and others when they pronounce that one person or another has "won" a debate. Very rarely does the media focus on the rational strength of the argument, but it is this that our critical thinking techniques are directed at.

RECONSTRUCTION

It is sometimes difficult to tell, when examining a peddler's entire presentation (i.e. everything he or she says, in a context of persuasion). whether or not we are being given an argument. The business of extracting an argument from such a presentation is called (Argument) RECONSTRUCTION. We refer to the unreconstructed presentation as the "raw material" of our analysis.

Inference Indicators
With luck, we will discover in our persuasion raw material certain words or phrases that provide a clue as to which statements are premises and which conclusions. These can be premise indicators, such as : and many others, which signal that an upcoming statement is to serve as a premise in support of another statement in the immediate vicinity.

Or we might find conclusion indicators, such as:

and many others, which signal that an upcoming statement is to be seen as a conclusion, relative to some premise statement in the immediate vicinity. Although few inference-indicating phrases are completely unambiguous (and could therefore lead us to things which are not part of an argument), they remain the best single clue as to the structure of a latent argument. Accordingly, your best first move in reconstructing raw material is to scan it for such indicators, and from them project your initial reconstruction of the argument therein.

Things become a bit trickier when there are no premise indicators at all. Then there are two possible strategies. Probably the best strategy is to find a statement to function as the conclusion of the presentation's as-yet latent argument. Sometimes such a statement (or rhetorical equivalent thereof) can be found among the sentences explicitly included in the presentation. If so, use it. If not, you'll have to construct one of your own (see below). Either way, here's how to proceed:

*Look over the presentation very thoroughly, to get the general drift.

*If necessary, pick up clues about the author's probable outlook or message from outside the presented material - from the biographical facts about the author, for example, or from what you can tell about the context of presentation. (If your raw material came from a speech given at a Klan rally, for example, the statement "We need to look beyond superficial differences and find the good in each individual heart," is probably not a good candidate for its conclusion statement.)

*Put together a short sentence which seems to summarize the one main message of the presentation, within the limits of outlook as indicated by the biographical and circumstantial information at your disposal. Ask yourself what declarative sentence this peddler would use to state the main point on an expensive billboard on the Interstate-- one that people have only a few seconds to read, at 70 mph.

*Look for such a statement, or the equivalent thereof, among the explicit sentences of the presentation. If you find one, that helps confirm that you're interpreting the presentation correctly. So call that sentence the conclusion, and go ahead with the analysis. If you can't find such a sentence, then review the above procedure in hopes of finding one which is confirmed. If this yields no better results, then just adopt your own formulation as the conclusion statement, and go ahead.

*Use that conclusion statement in subsequent steps of reconstruction and analysis, but remember that your "conclusion" here is a guess or hypothesis, and could be replaced by a better one if this one doesn't lead to a satisfactory overall reconstruction.

*Once you've picked an overall conclusion, revisit the raw material in search of statements which could function in a supporting role for that conclusion-- i.e. ones which the author could be giving in answer to the question "What makes you think so?" Repeat the process (and the imaginary question) in your search for further premises in support of those statements, and so on.

A second strategy is just to leap into the middle of the thing, pick any statement as a starting point, and keep asking those two very important logical questions:

a) What makes [the author] think so? This, as you can see, is a request for statements to function as premises in support of your target statement. So ransack the raw material until you find something to fill that requirement, then re-ask.

b) So what? This, for all its apparent insolence, can usefully be seen as a query as to what conclusion is to be reached, using the starting statement as a premise. Again, you ransack the material to find a statement which, at least apparently, was intended to fulfill that relative-conclusion role.

This strategy should not be your first choice, but it can sometimes allow a small ray of light to shine through an otherwise totally opaque presentation.

The Principle of Charitable Interpretation (Part I)
In some cases the best approach is to reconstruct as much of the argument as you can, and then try to determine what is missing by looking at the form (such as it is) of the argument as it is given, and supply the missing premises (and occasionally a missing conclusion). Here the core concept will that of VALIDITY, and the guiding rule will be the Principle of Charitable Interpretation. Validity is a key notion in the full formulation of the Principle, so the whole story will have to wait until the concept of Validity can be developed. But here are three important aspects of it:

a) Try to interpret a persuasion presentation as containing some argument structure, if it is at all plausible to do so.

b) Translate a peddler's rhetorical questions, exclamations, idiomatic expressions and the like, into appropriate and equivalent declarative sentences.

c) Avoid so far as possible a reconstruction that attributes to the peddler views she wouldn't really hold- that is, that identifies as premise or as conclusion some statement the author would reject.

Principle of Charitable Interpretation- (part II)
(Introduced by Cederblom and Paulsen) When reconstructing an argument which seems to be misordered or incomplete, we will want to give it the strongest possible interpretation we can. This is because we are interested in moving closer to the truth, not necessarily in "winning " an argument. If we interpret an argument in an intentionally weak way so that we can defeat it, we have not really done anything significant. It is only when we are able to successfully critique a strong argument that we can claim to have accomplished our aim.

This principle comes into play when it is not clear from the argument: what the conclusion is, what the premises are, or if any premises (or the conclusion) is missing. Based on the assumption that we are trying to find the most reasonable position to hold, the principle states that:

"When more than one interpretation of an argument is possible, the argument should be interpreted so that the premises provide the strongest support for the conclusion" pg. 12, text.

Validity
An argument is said to be valid if (and only if), when the premises are all true, the conclusion must be true too. To put it another way, an argument is valid if and only if there's no way the conclusion can be false without at least one premises being false too.

The term "Valid" refers to arguments, not to statements. Validity concerns the relationship between the premises and the conclusion, and not the actual truth values of the component statements at all. That is, it has to do with what combinations of truth values for premises and conclusion an argument will permit, not with what combinations actually do occur. So the fact that an argument has true premises plus a true conclusion does not tell us whether it is valid or not, since it does not answer the question of whether true premises plus false conclusion is a possibility for this argument (for some arguments it is, for others not.) The combination of false premises and false conclusion likewise does not give us a verdict about the validity of the argument- since it doesn't tell us whether the combination of true premises and false conclusion is a possibility. The combination of true premises and a false conclusion does tell us about the validity of the argument, since it does answer the relevant question. And since the answer is "Yes, this argument permits the combination of true premises and a false conclusion," the verdict is "No, this argument is not valid, since a valid argument would not permit that combination."

"Valid", then, is not a synonym for "Good"-- some valid arguments don't have a bit of truth in them, and some valid arguments composed totally of true statements are nevertheless worthless. All that its being valid tells us is that when and if the premises of this argument are ever all true, the conclusion is guaranteed to be true too. A valid argument is like a strong yet portable bridge: if you make sure that the premises are firmly planted on the truth, you can be sure that it will carry you over to a conclusion that is true too. If you proceed from false premises, however, there's no telling where the argument may take you.

Soundness:
In discussing arguments, we need to distunguish between deductive arguments- arguments where the truth of the premises will guarantee the truth of the conclusion and inductive arguments - those arguments where the truth of the premises will only make the truth of the conclusion highly probable or likely, but not certian.

Another way to identify a deductive argument is to refer to it as a Valid argument. As we read above, Validity refers to the formal structure of the argument- a valid argument is one in which the form is such that:

If it is possible for all the premises to be true and the conclusion to still be false, then you have what is called an Invalid argument. An argument could be invalid and still be a good Inductive argument, or it could be one which commits a Deductive fallacy. Once it is determined that an argument has a Valid form (it is a Deductive argument), the next step is to determine if all of the premises are indeed true. This is done in a variety of ways, depending on the type of premises we are dealing with. The different types of premises are discussed below, but for now, if all of the premises of a Valid argument are true, then the argument is said to be Sound as well as Valid. Only Deductive or Valid arguments can be sound or unsound.

Thus, an argument is sound if and only if :

Valid argument forms:
Modus Ponens- 

1. If A then B, 
2. A 
3. B (conclusion)

 Fallacious form: (affirming the consequent) 
1. If A then B, 
2. B 
3. A
Modus Tolens- 
1. if A then B, 
2. Not B 
3. Not A		 Fallacious form: (Denying the Antecedent) 
1. If A then B, 
2. Not A 
3. Not B
Disjunctive Syllogism- 
1. A or B 
2. Not A 
3. B		 Hypothetical Syllogism- 
1. if A then B 
2. if B then C 
3. if A then C
 

Using Truth Tables to discover Validity:

If you look at the structure of any deductive argument, you will notice that each of them can be expressed as a conditional statement, with the conjunction of all the premises serving as the antecedent and the conclusion serving as the consequent. With this in mind, we can use truth tables to find out the validity of different argument forms which do not match (immediately) any of the known valid forms.

Filling in Implicit Premises

1. Read what is there carefully to discern what the explicit premises are- (look at what you have already)

2. See if there is a conclusion that will follow from the premises given.

3. If necessary, provide such a conclusion, or re-word the given conclusion to make it more reasonable (retaining the meaning)

4. Look at the presuppositions of the premises so far for any additional implicit premises.

5. Avoid obviously false or questionable premises (unless they are explicit or a central presupposition of the argument.)

In short, there are two ways to see where and which implicit premises will need to be added:

Also- look for the simplest or most elegant expression of the implicit premise.

Be aware that not all arguments will be as simple as the ones we have been looking at. The formal structure of an argument in the wild will be complicated by (a) compounded compound statements (which will need to be broken down), (b) nested arguments which result in secondary conclusions which support the main conclusion- these arguments will need to be assessed on their own merits for validity and soundness.

Writing tips

(and things to look for in deciphering arguments in the wild)
Make sure that:

1. your conclusion is well stated and clear.

2. subordinate conclusions (if any) support the main conclusion.

3. your premises (reasons) support your conclusions.

4. the examples which illustrate your premises are not contradictory or questionable.

5. Any unfamiliar or important concepts are defined or explained- i.e. - using a word or term in a manner different from the usual (write to your audience).

Suggested form of prose arguments:

(paraphrased from Cederblom and Paulsen, pg. 42)-

a. Introduction- start with a non-controversial premise if possible.

b. First Section- (paragraph)- Reasoning for premise A

c. Second Section- Reasoning for premise B

d. Third Section (etc.,) Reasoning for Premise C (and so on)

E. Final Section- Present main argument in prose form, showing how all of the premises link together.

Suggested Activity:

Pick an argument and write a prose version of the given argument. Add in any needed premises or conclusions and give support for each of the premises. Follow the above pattern.

(for class review, depending on the number of people who actually did the assignment, divide them into groups based on which argument they chose, and have them collaborate on a single version of the argument. You can then compare in class this group version with the versions they came up with.

Roles statements play in arguments:

Up until now, all of the arguments we have seen included only:

(1) premises, and

(2) conclusions

But- arguments can also include statements which serve as:

(3) Descriptions: of a state of affairs- which may or may not lend support to the premises/conclusion. Descriptions can be used to :

(4) Explanations: of key concepts or terms, or of data (facts) appealed to in support of the premises or the links between them. Explanations seek to show why something occurred- and may involve descriptions- (but will reach conclusions that are not necessarily logical).

(5) Reports of Arguments: we can also find it useful, in giving an argument of our own, (or in reading one) to also give:

(6) Statements unsupported in the context: the writer could have intended these as premises/conclusions, or they could be evasive, but in general they are claims which either do not go with the argument, or are controversial and undefended.

(7) Summaries: these will be restatements of the argument or conclusion. These will either appear at the end of the argument or at the beginning.

(8) also- editorial comments, examples, illustration, analogies:

all of these may lend inductive support to the premises/argument, but will not provide deductivesupport.

We should note that all of the above statements will also use words which we have keyed on as premise or conclusion indicators- which may make things somewhat confusing. The trick here is to ask yourself "what is being argued for here, and how?" If the statements do not seem to be an argument, or part of one, then they may be descriptive. If the statements are not meant to convince you of a particular viewpoint or position, then it is not an argument.

Establishing the truth of premises: Conceptual vs. Empirical Premises
A crucial step in evaluating the soundness of an argument is determining the truth of the premises. The truth of a statement can be established by:
  1. personal experience,
  2. reference to an established authority,
  3. internal consistency, and
  4. consistency with the body of established fact (things we know are true already).
The most important step in determining the truth value of a given premise is determining if the premise is making a Conceptual claim or an Empirical claim. Premises which claim that some state of affairs exists or does not exist are considered Empirical premises. The truth of these premises will be established mainly by methods 1,2, and 4. above. On the other hand, the truth of some premises will depend on the meanings of some central words in the premise. Here, the statement is taken to present a Conceptual Theory - the author's idea of what concepts are crucial to the success of the argument. The methods for establishing the truth of these sorts of premises will be different from those used to establish the truth of Empirical premises. To illustrate, consider the following argument: Therefore, the "Weekly Enquirer" is bad journalism.

Premise 2 is an example of an empirical premise- it's truth or falsity is established by empirical means, which will often involve methods which rely on inductive arguments. (we could conduct a study to determine what people are more likely to believe or not believe. Premises 3 & 4 are conceptual premises - the truth or falsity of these premises will involve a discussion of what we generally mean by words like "deceptive" and what will count as "bad journalism". To further understand the different methods, we will first consider the process for evaluating conceptual premises, then look to the process for evaluating empirical premises.

Understanding more complicated Passages:

Keeping these things in mind, we can outline some steps to follow in reconstructing arguments:

Using and Criticizing Analogies in premises:

Analogies are used primarily as a means of explanation. In this way an analogy can serve one of two purposes.

In the first instance, an analogy can be used to argue (or convince) that something will have a characteristic based on its other characteristics. (i.e.- if an animal has a kidney, it has a heart, since all animals thus far found with kidneys also have hearts.)

In the second instance, An analogy is a comparison of one situation to another, with the purpose of clarifying certain points about the case in question by focusing on similar points in a more familiar case. In this sense, we focus on the similarities of the cases and try to ignore the (usually obvious) dissimilarities.

In either instance, a good analogy will:

  1. be clear and understandable- i.e.- somewhat more common to the understanding/experience of the audience than the argument in question. It should help us to better understand a complex issue or point.
  2. focus our reason on the relevant points of the claim being made- in short- the analogous situation should not be more controversial/complex than the situation it is intended to explain.
  3. preserve the relationship of the premises to the conclusion- the parallels drawn must be similar in all cases.
Most properly, the use of analogy takes advantage of our ability to see similarities in things. The analogy will claim that because thus-and-so has these properties, and this-other-thing also has similar properties, then because the former thing has this property, then the latter also does. For example: The Argument from design- OK- in this case we are supposed to ignore the obvious differences in size and complexity, and focus instead on the relationship between the function of the parts and the purpose which they (supposedly) evidence. This ignoring of the uncommon characteristics is legitimate if the characteristics ignored are indeed irrelevant to the comparison. In addition, there must be a genuine connection between the shared characteristics and the additional characteristic in question. I.E.- the comparison must hold in all cases- not just one.

The use of analogies can be fruitful either in an argument or outside of one. Inside of an argument, they can distance us from the emotional aspects of a topic so that we can focus on the relevant issues and make a more reasonable decision. (example- many of the analogies used in serious abortion arguments.)

Outside of an argument, we can use an analogy to better understand a difficult topic. In some cases, they can lead us to look at a topic or idea in a new way- one which may lead to new insights which prove valuable to our understanding of the topic. These new insights will have to be proven independently - we can't use the analogy to prove it, but it can be used to better understand it. (example- looking at the activity of the mind as being like the activity of a computer)

On the flip side, as with any of the argument techniques, an analogy can be used to deceive us or to hide facts from us, or even to confuse our thinking, therefore preventing us from discovering the truth. (many comparisons with the Nazis can be seen in this light).

To this end, we can now look at two ways to criticize or attack the use of an analogy:

again- need to focus on the similarities which are relevant to the truth of the premises- those which will make it more or less likely to be true.

We can- challenge the assertion that the conclusion is the result of the similarities- (example of the president being like the captain of a football team- You don't tackle the captain)

Technique #1- The goal of an administration is different from the goal of a football team- the goal of the administration is to make wise decisions, the goal of a team is to win game.

(this tactic questions the conclusion drawn from the stated goals - so- if we point to the dissimilarity of the goals- we see that the asserted conclusion (don't criticize the Pres) is less likely to be true- i.e.- effective in reaching the goal.

The tactic here is to point out a relevant dissimilarity between the two cases.

One type of analogy asserts a similarity between the two situations - But- we can attack or criticize this similarity as being incomplete or inaccurate. In short, there will be something which is left out or ignored which destroys the analogy- (prevents the conclusion from following in this case). Another type of analogy compares two situations and adds a further characteristic to one of them, which by analogy is supposed to hold of the second as well. This need not be the case.

For example- in the president/captain analogy, we can agree that we usually do not want to tackle the QB- but if they are running the wrong way- it may be extremely appropriate. In this case we accept the basic analogy, but disagree with the conclusion drawn from it.

Example Course Exercise: Analogies used in debates over Moral issues

Here is an analogy developed by J.J. Thompson's to address the moral permissability of abortion in a case of a pregnancy which is the result of rape: Instructors notes:

In this analogy, the violinist is supposed to represent the fetus, the music lovers society the rapist, and the fatal disease of the violinist represents the dependancy of the fetus on the mother .  Are all the relevant characteristics preserved?  (Have class decide) Would this same analogy work for other pregnancies that the mother wished to terminate?