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Arguments From Analogy

Arguments From Analogy
An argument from analogy is when we draw a conclusion based on comparing one thing to another.  Arguments from analogy are often used (but not always) to argue about a complex or poorly understood subject by comparing it to one that is less complex or better understood by the audience.  They are also often used to argue for a conclusion in a controversial case based on what is accepted in an uncontroversial case by claiming the characteristics of the cases are relevantly the same. 

One of the most popular analogies is between minds/brains and computers.  (As an aside, it is only an argument from analogy if a conclusion is drawn.  Sometime analogies are used merely as explanatory aids, not as vehicles for an argument.)

Perhaps the most famous argument from analogy is the the Argument from Design for the existence of God/gods.  There are many versions of this argument, but to give us a template, here's one:

P1.  The mechanics and inner workings of a watch are so mechanically complicated that they must have been designed by an intelligent being.  

P2.   Watches have a purpose so they must have been designed by an intelligent being.
C1.  As with a watch, life (or a particular organ or organism) is complex and has a purpose therefore, this necessitates that they had an intelligent designer.

HMC.  Therefore, intelligent God/gods exist.

Lets look at the underlying formal structure of an argument from analogy and show how to evaluate an argument from analogy within the context of this famous example. 

The formal structure of an argument from analogy looks like this:

P1.  Object 1 (or Set of Objects 1) and Object 2 both have properties p, q, r...

P2.  Object 1 (or Set of Objects 1) has property z.

HP*:  Properties p, q, r... are relevant to an object having property z. 

C.   Since Object 1 and Object 2 share properties p, q, and r and Object 1 has property z, then Object 2 must also have property z. 

We can also do a simplified version of the formal structure (in your argument evaluations, feel free to use either):

P1.  Object/situation 1 and object/situation 2 are alike in that they both have properties p, q, r.
P2.  Since we agree that object/situation 1 has property z (e.g., it is good/bad, legal/illegal, should do it/shouldn't do it).
C.  Therefore, since object/situation 2 has the same relevant properties as object/situation 1, we should apply the same judgment to object/situation 2 (i.e., it has property z).

We can more explicitly formalize the argument from design to see how the argument from analogy works.

P1:  Known complicated things such as a watch have the property of having being designed by something intelligent.

P2:  Known complicated things (e.g.,  a watch, a computer)  have the property of "purposefulness" and therefore have the additional property of having being designed by an intelligent designer. 

P3:  Life or individual organs or organisms have the properties of complexity and have purposes.

HP*:  The properties of complexity and purposefulness are relevant to an object having the property of having a designer. 

C1:  Therefore, life also has the property of being designed by something intelligent,

MC:  That intelligent thing must be God/gods, therefore God/gods exist. 

Evaluating Arguments from Analogy

When evaluating arguments from analogy, most of our attention will be on the hidden premise, that having properties p, q, r are relevant to having property z.  To see how this works lets turn to the argument from design:  The most famous refutation of this argument comes from Hume in the 18th Century.  Hume gave 6 main criticism of the argument most of which are in some way related to evaluating the hidden premise.  We'll look at a few of them. 

We should now ask whether the property of complexity is necessarily relevant to also having the property of having an intelligent designer.  One way to approach this is to look for counter-examples;  that is, examples of things that are complex but (to our best knowledge) don't have a creator.   Are snow-flakes intelligently designed? (Is someone up in the sky furiously making them every time it snows?)  What about complex cloud patterns?  What about those swirls in your coffee?  It seems, we can have complexity without a conscious intelligent designer.

The question of purposefulness is a separate one.  I will simply note that it will take substantial argument to show that each life was designed for some sort of cosmic purpose.  

So, in a nutshell the counter to an argument from analogy hinges on showing that having one set of  properties (p, q, r, z) doesn't mean that every object with properties p, q, and r will also necessarily have property z. 

In the case of the argument from design, another major flaw is that there is a disanalogy between inanimate objects which are unable to pass on complexity and living organisms which are able to reproduce and pass on complexity (and possibly become more complex over time).  Disanalogies arise when we show that the properties under consideration (complexity and purposefulness) aren't necessarily relevant to having some other property (intelligent designer). 

Lets look at one more example of an argument from analogy (intentionally bad--do not try this at home!) 

P1.  Water is clear, liquid, and quenches my thirst.

P2.  Gasoline is also, clear and liquid. 

HP.  The properties clearness and liquidity are relevant to an object having the property of "thirst quenchability."

C.  Therefore, drinking gasoline will quench my thirst.  

If you've been paying attention you might be able to figure out what's gone wrong... The problem is with the hidden premise.  There is a disanalogy between water and gasoline because clearness and liquidity are not necessarily relevant to something having the property of being able to quench thirst.  

In the policial sphere we often see arguments from analogy with concern to gun policy.  On the anti-gun control side we see analogies with policy in Switzerland (which has lax restrictions on what types of guns can be owned).  On the pro-gun control side we often hear analogies with policy in Australia (which banned assault weapons).  The rebuttals to both arguments from analogy often involve claims to the effect that there are cultural elements that aren't relevantly similar between the US and the other country.  

List of Common Fallacies

Here's a list of common logical fallacies.  Some of which we discussed in class.  We'll discuss more in the future.  Here's a link to a handy fallacy guide with explanations.  Wikipedia is also a good source for explanations of the various fallacies as well as the cognitive biases.

Naturalistic Fallacy (3 types)  (a) Natural is better, (b) that's the natural order of things (i.e. for moral arguments), (c) ascribing natural properties not non-natural things.
Argument from authority/antiquity/ancient wisdom/tradition
Ad populum
Appeal to emotions (usually pity, sympathy, fear, guilt, or disgust)
Genetic fallacy
Argument from personal incredulity
Ad hominem
Poisoning the well
Tu quo que
Ad hoc rescue
Moving the goal posts
False dilemma
Perfectionist fallacy/negative confirming instances: sub-category of false dilemma
Post hoc ergo proptor hoc (confusing correlation with causation)
False premise
Non-falsifiable hypothesis
Subjectivist fallacy
Hasty generalization
Red herring
Strawman
Non-sequitur
Begging the question
Texas sharp shooter fallacy (also considered a cognitive bias)
Appeal to force
Two wrongs fallacy
Confirming instances fallacy (related to confirmation bias)
Argument from Ignorance/inappropriate burden of proof/demanding proof a negative


Biases and Cognitive Biases:
Appeal to anecdote (also could be categorized as a fallacy)
Confirmation Bias
Selection Bias
Motivated Reasoning
Negativity Bias
Halo effect
Bottom line effect

Arguments from Analogy: Lecture Links

Science is just another religion.  [Implied conclusion?]

"America should declare war on Syria now.  We didn't stand and let Hitler do what he pleased in WWII, did we?"

Taxation is like slavery.

Argument from Design

• 1. Every time I have encountered a complex machine, it has been the result
• of an intelligent creator.
• 2. Similar effects prove similar causes.
• 3. The universe is similar to a complex machine.
• 4. Therefore, the universe is a result of an intelligent creator. 

Religious liberty, employer health care plans, birth control

Orca and Danger/Stress: