Common Argument Structures: Arguments from Analogy

+ Overview: Literary Analogies vs Arguments from Analogies

There are two kinds of analogy structures which we can distinguish according to their purpose. Arguments from analogy are used to argue for a conclusion: since two things are alike in one respect, therefore they must be alike in some other respect. Literary analogies, on the other hand, are not arguments. They are observations that two things are alike in some interesting way.

Examples of Literary Analogies (used to compare two things)

1. You are as annoying as nails on a chalkboard.
2. Your smile is like the sun.
3. He's like a rock.
4. Life is like a box of chocolates. You never know what you're gonna get.

++ Evaluating Arguments from Analogy
Before evaluating an argument from analogy we have to understand its structure.

Formal Structure:
(P1) A and B share attributes w, x, y.
(P2) Attributes w, x, and y are relevant to/predictive of having attribute z.
(P3) A has attribute z.
(C) B has attribute z.

In normal speech, people rarely explicitly list the ways in which two things are alike as in (P1); it's usually implicit. (P2) is almost always implicit but it is the most important premise in terms of evaluating the strength of the argument. (P3) is often explicit. Now that we understand the components, let's look at how we evaluate this kind of argument.

Common Uses:
Arguments from analogy are often used to argue that
(1) a new policy/idea/plan will or won't work because it shares relevant characteristics with a previous policy/idea/plan;
(2) a something is good/bad/beautiful/ugly (i.e., value judgements) because it shares relevant characteristics with something we ascribe those same values to.

A 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).

Evaluating Analogies:
As with any kind of argument, the best way to evaluate an analogy is to rewrite it into its standard form as ask yourself if each premise is true. The strength of an analogy usually rests upon the truth of (P2).

Here are the main steps you can use to evaluate an analogy:
Step 1 Is (P1) true? In some analogies, (P1) won't be explicitly stated so you'll have to infer what it is. In most cases, however, it will be stated. Let's look at an example:

E.g., Gas and water are both transparent and liquid, therefore they will both taste delicious.

(P1) of this argument is that "gas and water share the attributes 'transparent' and 'liquid'. The premise is true. As you might have noticed, there is a bad inference going on, so let's look at that next when we evaluate (P2).

Step 2a Is (P2) true? Essentially, in this step we're asking if the two things being compared share similarities that are relevant to the conclusion being true? The more relevant similarities there are, the more likely the it is that the analogy is strong and that the conclusion is true. Let's look at a slightly different example from above.

E.g. Gasoline is almost as transparent as water and it's also a liquid. Therefore, if I fill this glass with gasoline, I'll be able to see through it.

(P2) of this argument will be something like "being transparent and being a liquid are predictive of being see-through". Being transparent is but being liquid isn't because not all liquid can be seen through.

Step 2b Evaluating relevant dissimilarities in (P2): In this step we really want to think hard about what the analogy is trying to convince us of. We want to go beyond the similarities offered in the argument and think for ourselves for a moment. Are there many relevant dissimilarities between the two things being compared? The more relevant dissimilarities there are, the weaker the analogy. Suppose the same analogy as above but for a different conclusion.

E.g., Gasoline is almost as transparent as water and it's also a liquid. Water is a delicious drink, so gasoline must be too.

Relevance is a measure of how well premises support the likelihood of the conclusion being true. In this argument gasoline and water are similar in the way suggested but these similarities aren't relevant to the conclusion. Something being transparent and liquid doesn't increase the likelihood that it will be delicious to drink. In terms of the attributes relevant to whether we think something will be delicious, gasoline and water are extremely dissimilar. Here is a relevant dissimilarity: gasoline is a poison, water is not.

Step 3 Number of Instances Being Compared: Here we're also evaluating (P2). We're looking to see how strong the relationship is between having a certain set of properties and some other property. The greater the number of instances being compared to establish the relationship between w, x, y and z, the stronger the analogy. To see how this works, let's look at the teleological argument:

Teleological Argument: A watch is a mechanism of exquisite complexity with numerous moving parts precisely arranged and accurately adjusted to achieve a purpose, a purpose imposed by the watch's designer. Likewise, the universe has exquisite complexity with countless parts, from atoms to asteroids, that fit together precisely and accurately to produce certain effects as though arranged by a plan. Therefore, the universe must also have a designer.

E.g., In the teleological argument we can apply the reasoning not just to watches to show that 'complexity' is predictive of having a designer, we can come up with many instances that confirm this principle (e.g., computers, cars, houses, etc…).

Since we can come up with many kinds of things that have a certain set of properties (i.e.., complexity, moving parts precisely arranged and accurately adjusted to achieve a purpose) it is a strong inference that such things will also have some other property (having a designer).

The generalized pattern looks like this:
E.g., Object 1 has properties w, x, y, and also z. Object 2 has properties w, x, y, and also z. Object 3 has properties w, x, y, and also z. (HP3) having properties w, x, y is strongly predictive of having property z. Since Object 4 has properties w, x, y (C) it must also have property z.

Classically, the teleological argument doesn't fail in this respect but because of reasons having to do with Step 2b and Step 4. Can you figure it out?

Step 4 Diversity Among Cases: The greater the diversity among cases that exhibit the relevant similarities (i.e., establish that properties w, x, y are relevant to having property z), the stronger the argument.

A 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).

Examples of Arguments from Analogies

1. Empty your mind, be formless. Shapeless, like water. If you put water into a cup, it becomes the cup. You put water into a bottle and it becomes the bottle. You put it in a teapot, it becomes the teapot. Now, water can flow or it can crash. Be water, my friend.” ― Bruce Lee

2. Being a good critical thinker is like being a good musician. The more you practice, the better you get. (HC) So, if you want to be a good critical thinker, you need to practice a lot.

3. Cheerleading should be considered a sport. Cheerleading requires strength, flexibility, hard training, and a high level of fitness.

4. Teleological Argument: A watch is a mechanism of exquisite complexity with numerous moving parts precisely arranged and accurately adjusted to achieve a purpose a purpose imposed by the watch's designer. Likewise, the universe has exquisite complexity with countless parts, from atoms to asteroids, that fit together precisely and accurately to produce certain effects as though arranged by a plan. Therefore, the universe must also have a designer.

5. Cosmological Argument (variation): A house couldn't have always existed and spontaneously appeared out of nothing, therefore the universe couldn't have always existed and spontaneously appeared. Since the house needs a builder to explain its existence, so does the universe.

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