Another form of inductive reasoning is known as reasoning by analogy. Basically, an analogy is a statement of a logical relationship between two similar things that are compared with each other. An argument by analogy is presented in the form of “A is like B,” or “X is similar to Y.”

Consider the following simple question: “Is an apple more like an orange or a banana?” Although everyone probably knows the differences between these three types of fruit, just how would we go about making a valid analytical comparison of them? Analogical reasoning seeks to identify specific sets of similar and dissimilar characteristics, in search of some unique combination of characteristics that can then be used to define distinctive properties of each set.

EXERCISE 2. In this Exercise, we will use the simple question from the example, supra, to demonstrate how "reasoning by analogy" works. Begin by first trying to identify as many different similarities and distinctions among these three items as possible.

For example, obviously, all three items are edible fruits, so this characteristic would not be particularly useful in trying to identify a unique distinction among these three fruits. So, we may want to consider a few other characteristics.

(1) Seeds. They all contain seeds inside their fleshy fruit part. In two of these fruits (i.e., the apple and the orange) the seeds are NOT generally eaten at all, but in the third fruit (the banana), the seeds are so tiny that they are normally eaten along with the fruit itself.

(2). Color. Color is probably not a particularly good characteristic to use in trying to distinguish these fruits. Although the color of ripe oranges and ripe bananas is usually quite distinctive, ripe apples typically range from green to yellow to red and even orange.

(3). Shape. Shape is another way to differentiate among at least some of these three different fruits. Both apples and oranges are typically more round in shape, whereas bananas are never rounded; instead, they are more elongated in shape.

(4). Outer Skin.

(a). The outer skin of oranges and bananas can be peeled away from the inner flesh of the fruit without the aid of a knife, but the outer skin of an apple can only be removed with the aid of a knife or some other sharp object.

(b). Also, the outer skin of apples is sometimes eaten along with the fruit (but not the apple seeds), whereas the outer skin of both bananas and oranges is never eaten.

(5). Citrus Family. Finally, oranges are a member of the citrus family of fruits, whereas apples and bananas are not.