[Critical Thinking] Elements of Reasoning Chapter 7: Argument by Analogy and Models

Argument by Analogy and Models

To draw an analogy is to call attention to specific similarities between two distinct subject matters. In an argument by analogy, these similarities are used as support for the conclusion. A model is a special case of argument by analogy, and is typically used in the sciences.

The form of an argument by analogy:

Analogy:

Analogies used as arguments:

An analogy is a comparison of two or more things alike in specific respects. In literature, science, and everyday conversation, analogies are often used to explain or describe things. A couple examples:

As cold waters to a thirsty soul,

so is good news from a far country.

• Proverbs 25:25

... the evening is spread out against the sky

Like a patient etherized upon a table ...

• T. S. Elliot

An argument by analogy has the following form:

A is similar to B (C, D, ...) in possessing features 1, 2, 3, ...

A also possesses feature N.

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So, B probably possesses N as well.

Note that this is a nondeductive argument, so the premises support but do not prove the conclusion; all of the premises may be true and the conclusion may still be false.

Adult humans and complex robots each possess the ability to speak intelligently, perceive, move about, and solve complex problems. Adult humans are also conscious. But if adult humans and complex robots are so alike in so many different and important ways, then what reason do we have for thinking that they are not conscious in just the same way?

In this case, two claims are made:

1) Humans and robots are similar in certain ways.

2) Robots are probably similar to humans in a specific way.

How to evaluate an argument by analogy:

A famous example:

Detecting Design:

Enthymemes

In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there; I might possibly answer, that, for anything I knew to the contrary, it had lain there forever: nor would it perhaps be very easy to show the absurdity of this answer. But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place (...) There must have existed, at some time, and at some place or other, an artificer or artificers, who formed [the watch] for the purpose which we find it actually to [have, and] who comprehended its construction, and designed its use. (...) Every indication of contrivance, every manifestation of design, which existed in the watch, exists in the works of nature; with the difference, on the side of nature, of being greater or more, and that in a degree which exceeds all computation.

— William Paley, Natural Theology (1802)

We often make arguments by analogy without even knowing it because we state them as enthymemes. Consider this example:

Look at poor ol' Rex just lying there. He hasn't been the same since Billy went off to college; he must be depressed.

This is actually an enthymeme

of an argument by analogy.

Can you see how?

Both a watch and a eukaryote cell possess features that indicate contrivance and manifest design.

The watch has a further feature, namely that it is in fact the product of an artificer or artificers.

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So, the cell probably has this feature as well; it is probably the product of an artificer or artificers.

On depressed dogs:

This brings up an interesting point.

Animals and Superheroes.

Some fictional characters are similar to animals in possessing features like immunities to pain, disease and even aging, as well as the ability to survive extreme environments normal humans cannot. We often refer to characters with these features as Superheroes. What sorts of animals also possess these features?

It seems that in order to understand

what's going on in the mind of any non-

human animal (or any non-

communicative human), we can only

use analogy to our own experience

and the experience of our cohorts.

It's a good thing, then, that we have access to the experiences of all our cohorts!

Wait...

If the above is an analogy, then it's because we are comparing Rex's behavior to the behavior of a person who we know is depressed (colloquially, if not clinically) about something.

Rex moaps around, is lethargic, doesn't seem to be as happy as he was before, etc. These are behaviors that people who are in a funk display as well, and we know that they are sad about something because they can tell us about it. Rex can't talk, but his actions (behaviors?) speak loud enough: he's depressed!

Once we've identified an argument as an argument by analogy, we'll want to evaluate it. Here are some steps:

1) Identify what's being compared.

2) Identify the conclusion.

3) Check for relevant similarities and dissimilarities.

4) ???

5) Profit.

Models:

Material models:

Formal models:

Drosophilia:

Drosophilia melanogaster (the fruit fly) is probably the most common scientific model in the fields of genetics, physiology, microbial pathogenesis, and life history evolution.

Why might this be?

Similarities and Dissimilarities:

Analogical reasoning in the natural and social sciences often takes the form of using models to reach conclusions. A model is a familiar and well understood system used to represent a system not as well understood.

We assume that features of the model are similar to those of the unfamiliar system, and we extend conclusions about the model to it.

Models are EVERYWHERE in the sciences. There are two kinds (that we'll talk about).

A formal model is a set of concepts and principles belonging to one system employed to develop an understanding of another system.

For example, Charles Darwin used the

concepts of unconscious and conscious

selective breeding, which was well

understood, to explain his theory of

natural selection, which was not well

understood at the time.

For any set of things we might want to compare in an analogy there are going to be a number of ways in which they are alike and different from one another. When we critique or construct an argument from analogy though, only the relevant ways matter.

Thinking back, does it matter to our analogy that Rex has a particular color of fur? What about that he is a dog?

A material model is a physical system that is taken to represent parts of another physical system. The representation is based on the assumption that the systems share enough features to allow us to extend discoveries about the model to the system it models.

The most familiar material models are lab animals. We use lab animals as a 'stand in' for a human subject because they are similar to us physiologically and because an experiment on a human subject wouldn't pass IRB.

Relevant similarities:

What's relevant?

Of mice and men.

Relevant dissimilarities:

saccharine

A similarity is relevant only if it gives us reason to accept that the conclusion follows from the analogy.

A dissimilarity is relevant only if it gives us reason to doubt that the conclusion follows from the analogy.

How can we tell which

similarities and dissimilarities

are relevant though?

What are some relevant similarities and dissimilarities between the two things being compared in the argument below?

Both a watch and a eukaryote cell possess features that indicate contrivance and manifest design.

The watch has a further feature, namely that it is in fact the product of an artificer or artificers.

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So, the cell probably has this feature as well; it is probably the product of an artificer or artificers.

When scientists wanted to know what effects saccharine, an artificial sweetener, would have on humans, they turned to the trusty lab mouse.

However, some scientists

objected on the grounds that

mice metabolize the substance

differently than humans, and therefore were poor models.

Determining relevance:

There isn't really a helpful answer to this question. Relevant similarities and dissimilarities are just those similarities and dissimilarities that give us reason to accept the conclusion or doubt the conclusion, respectively.

However, this does not mean that just ANYTHING can be considered a relevant similarity or dissimilarity, since the claim that X is a relevant similarity/dissimilarity will have to be defended with an argument if it is challenged.

'unconscious' selection

'conscious' selection

'natural' selection