Reasoning by analogy

Learning how to reason by analogy is one of the most important objectives of legal education.  But you certainly don’t have to be a lawyer to use analogy in your thinking.  In fact, whenever we encounter a new situation, we start searching for some familiar elements in it to give us an indication what to do.  In law school, you have to build awareness of what is going on in your head when you reason by analogy.  In other words, you deconstruct the process.  Generally, when you reason by analogy, you take the following steps:

1. Identify the analogy by recognizing the similarities between objects or situations.  Let’s say, you see a tangerine for the first time and you want to compare it to oranges, lemons, and peaches that you are familiar with.  We like to think in big categories or archetypes, so the first thing that probably jumps out is that they are all fruits, and the tangerine is just like an orange or a lemon because it is a citrus. 
2. State the purpose of the analogy.  The purpose allows you to determine what characteristics are essential.  In the above example, if your purpose is to avoid citruses because of the allergies they may cause, the attribute of being a citrus is essential and your analogy between the tangerine and the orange or lemon is good.  Now, let’s say, you want to know how easy it is to peel off the skin of the fruit.  If that’s the case the analogy between the tangerine and orange is still good, but the analogy between the tangerine and lemon becomes weak because it’s hard to peel a lemon. If you compare the sweetness of the fruits, the tangerine becomes more like a peach than a lemon.
3. Assess the source of your analogy.  If there are alternative sources of comparison, how do you choose which to use? Let’s say, in my last example, which focused on the sweetness of the fruits, I could use kiwis as another basis of comparison but I chose not to.  What is the significance of my choice?  Is there a difference in the perceived sweetness when I say, “Tangerines are just like kiwis,” and when I say, “Tangerines are just like peaches”?
4. Evaluate the ambiguities, dissimilarities, false attributions that may weaken or break the analogy.  Do the differences between the tangerines and peaches undermine the analogy?  What are the underlying assumptions when you make the comparison?  In the example above, I assumed that I was comparing ripe fruits, otherwise, the analogy wouldn’t make sense.   If you hear the sentence:  “This toy is a lemon,” does it mean that the toy is defective or it shares some attributes with the fruit?   

For additional sources on reasoning by analogy, check out LawNerds and Analogy and Precedent from the Bridge site. 

To test yourself, do Analogy Exercises by Peter Suber.  For some practice in pattern recognition, try Brain Workout for Your Frontal Lobes from SharpBrains.