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.
     In this example, we will first try and identify as many different similarities and distinctions among these three items as possible. To begin with, all three items are edible fruits. They all contain seeds inside their fleshy fruit part. In two of these fruits (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. Color is probably not a particularly good characteristic to use in distinguishing these fruits. Although the color of ripe oranges and bananas is usually quite distinctive, ripe apples typically range from green to yellow to red and even orange. Both apples and oranges are typically round in shape, whereas bananas are never rounded; instead, they are more elongated in shape. 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. 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. Finally, oranges are a member of the citrus family of fruits, whereas apples and bananas are not.

     To more easily understand these various distinctions, we can incorporate the results of our analysis into the following chart:

     In making our final comparison, we then attempt to determine in which of these categories apples and oranges are most alike (i.e., similar). Of all the categories that we have compared, apples and oranges are similar only in that they are both generally round in shape and their seeds are not edible. In all other categories of our comparison, apples and oranges are dissimilar.

     Comparing oranges with bananas, we find once again that these two fruits are similar in only two of the categories that we examined (i.e., they are both peelable without the aid of a knife and they both have inedible skin). Finally, comparing apples to bananas reveals only one similar characteristic between these two fruits: neither belongs to the "citrus" family.

     In this example, the final category, "color," is not useful for any meaningful comparison, so we will not consider it any further. Reasoning by analogy, we thus can conclude that an apple is more like an orange than a banana as to its overall shape and the fact that its seeds are inedible (like those of an orange). Likewise, an apple is more like a banana only in the fact that both of these fruits are not members of the citrus family of fruits.

     Remember the original question: "Is an apple more like an orange or a banana?" Reasoning by analogy we can only conclude: "It depends!" Specifically, our answer to this question depends entirely upon which set of criteria we are using to make our comparisons.

     The foregoing example is illustrative of a very important aspect of any legal reasoning that is made by analogy: the relative degree of similarity between two things is entirely dependent upon what specific category of data the comparison is based upon. Comparing apples, oranges, and bananas can produce entirely different results that are not dependent upon the individual items compared, but upon the specific categories that we select for making those comparisons. This unique feature of reasoning by analogy makes this form of argument particularly well suited for legal analysis because it can be asserted to prove (or to disprove) almost any given set of comparisons. However, it also makes this form of argument far less reliable than the traditional logical syllogism argument or even than an argument based upon deductive reasoning.

     Continuing with our fruit example, suppose that in your jurisdiction (State X) there is a statute (i.e., Statute 101) that prohibits "the transport of oranges and similar fruits into the State of X." (emphasis supplied). You have been contacted by an apple grower who wants to ship a large order of apples into State X, but he is concerned about violating this statutory prohibition which is punishable by payment of a large fine for each violation. After researching the law, you find a second statute (Statute 202), also from State X, that expressly permits "bananas and similar fruits" to be imported into State X. (emphasis supplied). To answer your client's legal question, you are now faced with the very problem that we have been considering in our fruit example: "Is an apple more like an orange or a banana?" Reasoning by analogy what specific argument would you make on behalf of the apple grower?

     Based upon our previous analogical analysis, you first focus upon the meaning of the phrase "and similar fruits" that is used in BOTH statutes. This phrase is the common term that will be used as a bridge for your deductive syllogism argument. The only basis for making a favorable comparison between apples and bananas would be to assert that neither fruit is a member of the citrus family. Your syllogism might look like this:

(1) Statute 101 prohibits the shipping of ALL "oranges and similar fruit" into State X.
(2) Apples and oranges are NOT similar fruit, because oranges are citrus fruits and apples are not.
(3) Therefore, Statute 101 does NOT prohibit the shipping of apples into State X.

     By contrast, attorneys for State X would argue that since apples and oranges are both round and both contain inedible seeds, they are "similar fruits" and thus prohibited by the very same statute (i.e., Statute 101). The State's syllogism argument might look like this:

(1) Statute 101 prohibits the shipping of ALL "oranges and similar fruit" into State X.
(2) Apples and oranges ARE "similar fruits," because they are both round and they both contain inedible seeds.
(3) Therefore, Statute 101 prohibits the shipping of apples into State X.

     BOTH of these arguments are logically sound. Both are also supported by facts that have been reasoned by analogy with reference to the meaning of the statutory phrase "and similar fruit." Still, only one of these very opposite conclusions can be right. The other conclusion is wrong, even though both arguments are based upon sound analogies. How do we determine which analogy should be applied?

     This example illustrates the major obstacle to legal analysis that is presented by the use of reasoning solely by analogy. In legal analysis, arguments by analogy look for specific similarities (or dissimilarities) between ANY two things that are being compared with each other. Care must be taken, however, in selecting and articulating which specific individual criteria form the basis for making a LEGALLY RELEVANT comparison. Arguments by analogy do not attempt to declare general conclusions. They only seek to establish the comparative identity (by analogy) of individual facts or circumstances. The attorneys, and the courts, must determine which of all possible criteria that might be compared in a given circumstance are most appropriate. These criteria are said to be the ones that are legally relevant. All other criteria, although useful for making other comparisons in other cases, are unimportant to the case at hand. However, they are NOT legally relevant.

     Conclusions reached by analogical reasoning, unlike those based upon inductive reasoning, are not supported by a commonality of similar experiences in similar situations; instead, they are based upon the degree to which one individual circumstance or result is similar (or dissimilar) to another. If two different things are only partially similar, then the comparison between them can only be partially accurate. The greater the number of materially relevant points of similarity that can be described between two different things, the greater the effectiveness of the resulting comparison. This can be illustrated in the following manner:

(1) Facts A, B, and C all produce the same legal consequence, X.
(2) Facts A and B also produce a different legal consequence, Y.
(3) Therefore (reasoning by analogy) Fact C PROBABLY will also produce the legal consequence, Y.

     There is nothing in this argument that says anything specifically about the relationship between Fact C and legal consequence Y. Our conclusion about legal consequence Y is derived only by Fact C's analogy with Facts A and B in situations that produce an entirely different legal consequence, X. Any conclusion that we might derive from Fact C's similarity with Facts A and B, and their relationships with legal consequence X, may or may not have the same relationship to legal consequence Y, the thing that we actually want to establish in our conclusion. For this reason, arguments by analogy may be helpful in establishing the validity of a particular legal premise (e.g., that Fact C probably will produce legal consequence Y), but such arguments, by themselves, generally cannot produce the same level of confidence as a true legal syllogism would.

     Ultimately, our confidence in the accuracy of the conclusion that "Fact C PROBABLY will produce the legal consequence, Y" is in part based upon the number of similar points of comparison that we can make between Fact C and Facts A and B. Thus, if we are able to find other similarities between these same Facts, then our confidence in this specific conclusion would be greater.
To illustrate the relationship between an argument by analogy and a deductive syllogism within the context of an actual legal argument, consider the following example:

(1) A Battery may be simply defined as the intentional, nonconsensual contact with the person of another that is either harmful or offensive.
(2) Defendant intentionally and without consent struck the Plaintiff's pet puppy with a stick, causing harm to the puppy.

     Has the Defendant committed a Battery? The answer to this question is uncertain. We cannot construct a syllogism because we do not have any two terms in either the major or the minor premise that are equivalent with each other. In other words, there are no transitive terms that logically bridge or connect the major and minor premises. Specifically, in this example, we have the term "the person" in the major premise, and a completely different term, "the puppy," in the minor premise. What we need to know is whether these two terms "person" and "puppy" may be treated as equivalents for purposes of applying the syllogism. This is where the argument by analogy may be helpful in resolving this question.

     We begin by looking for Battery cases involving puppies. Unable to find such a case, however, we do find several other cases that we will use to construct our argument by analogy.

Case A: The court upheld a Battery action on behalf of a person who was struck and injured by a stick that was intentionally swung by the defendant without the victim's consent.

Case B: The court refused to permit a Battery action against a defendant who intentionally and without consent threw a rock and struck the plaintiff's dog, injuring the dog.

     We first reason by analogy, comparing the two different cases. Cases A and B BOTH involve actions for Battery, although the offending agent in Case A was a stick, whereas Case B involved a rock. Initially, we conclude that for purposes of a Battery there is probably no legally significant difference between a stick and a rock, so we look for some other reason to explain the different results in these two cases. Analogical legal reasoning seeks to determine whether the "puppy" in our case is more like the "person" in Case A or the "dog" in Case B. Comparing Case A with Case B, we conclude by analogy that a puppy is MORE LIKE the "dog" in Case B than the "person" in Case A. But how does this help us construct our syllogism?

     We are still no closer to answering our initial question than we were before. Even after concluding by analogy that the "puppy" in our case is more like the "dog" in Case B than the "person" in Case A, we still do not have an answer to the question of whether the Defendant in our case has committed a Battery or not. All we know from our reasoning by analogy is that intentionally striking the "dog" in Case B was not a Battery, whereas the intentional striking of the "person" in Case A was a Battery. Again reasoning by analogy, we might further conclude that a "puppy" is NOT a "person," at least for purposes of imposing liability for a Battery. This conclusion is a little more useful than our first conclusion, but by itself it still does not answer our question: has the Defendant in our case committed a Battery? To do this we must return to our original syllogism. However, this time we can substitute the new information that we have determined by analogical reasoning from our analysis of Cases A and B:

(1) A Battery may be simply defined as the intentional, nonconsensual contact with the person of another that is either harmful or offensive.
(2) Defendant intentionally and without consent struck the Plaintiff's pet puppy (which is NOT a person) with a stick, causing harm to the puppy.
(3) Therefore, Defendant has NOT committed a Battery.

     Just as always, our ultimate conclusion was attained deductively through application of a typical logical syllogism argument. However, we reasoned by analogy to help us compare the equivalency of two different terms (i.e., person and puppy) that were initially contained within the major and the minor premises. Without the aid of this type of reasoning, we could not have completed our logical syllogism because the terms in the major and minor premises were so completely dissimilar (i.e., puppies cannot be compared with people). Thus, we used reasoning by analogy as an AID to developing premise statements that were similar; these statements were then used to construct our logical syllogism argument. Despite the usefulness of reasoning by analogy, it must be observed that analogical reasoning, by itself, is NEVER a proper substitute for syllogistic argument. It is merely one of many tools that may aid in the development of such an argument.