An enthymeme is an argument in which one of the premises or the conclusion is not explicitly stated.  Usually, this is because the unstated claim is obvious.  Enthymemes are perfectly acceptable if used properly.  But sometimes, they can be used incorrectly to draw a false conclusion.  This can happen when the unstated claim is actually false.  Such examples are frequently found in debates over origins or faith systems.  So, understanding enthymemes can be extremely useful in apologetics.

A classic example of an enthymeme is the following:

Socrates is a human.  Therefore, Socrates is mortal.

The unstated premise is “all humans are mortal.”  Since this is obvious, it was reasonable for the person making the argument to leave it unstated.  When the argument is fleshed out and the missing premise is supplied, we can see that this is a good argument:

  1. All humans are mortal. (the major premise, previously unstated)
  2. Socrates is human. (the minor premise)
  3. Therefore, Socrates is mortal. (The conclusion)

The above is a categorical syllogism.  It has two premises and one conclusion and deals with categories.  The conclusion puts some or all of one category within or outside of another category by linking both to the middle term.  The middle term is that which is found in both premises.  So, in the above example, the middle term is “human.”  Both the major term (“mortal” in this case) and the minor term (“Socrates” in the above example) must be linked in some way to the middle term so that they can be linked to each other, either in a positive or negative way.  In this case, Socrates does indeed belong in the category of “mortals” because he is human and all humans are in the category of mortals.  An enthymeme can be identified by supplying the missing premise.

Consider the following example.  “You shouldn’t smoke.  It’s bad for your health.”  In this example, the conclusion is stated first “You shouldn’t smoke.”  One supporting premise is supplied: “[Smoking is] bad for your health.”  But a third unstated premise must be supplied in order for this argument to be valid.  The person is arguing that “smoking” belongs in the category of “things you should not do” by pointing out that smoking falls in the category of “things that are bad for your health.”  The only way this follows logically is if we add the unstated premise “things that are bad for your health” are in the category of “things you should not do.”  So, when fleshed out the argument is:

  1. All things that are bad for your health are things you should not do. (The major premise, previously unstated).
  2. Smoking is a thing that is bad for your health. (minor premise)
  3. Therefore, smoking is a thing you should not do. (conclusion)

Note that even though the major premise was originally unstated, it must be what is supplied above otherwise the conclusion would not follow logically from the minor premise.  In other words, the only way we can logically argue that smoking belongs in the category of “things you should not do” on the basis that it is “bad for your health” is if all “things bad for your health” fall into the category of “things you should not do.”

As in all categorical syllogisms, only by linking both the major term (things you should not do) and the minor term (smoking) to the middle term (things that are bad for your health) can they be linked to each other.  To spot an enthymeme, think what additional claim must be made in order for the conclusion to be logically justified.

In some cases, an enthymeme leaves the conclusion unstated.  Suppose someone said, “Decent people apologize for their mistakes, and you are a decent person.”  The conclusion, “You should apologize for your mistakes,” is probably obvious enough that it does not need to be stated.  That’s an appropriate use of the enthymeme.  In fact, sometimes an argument is more persuasive if the conclusion is unstated; this encourages the listener/reader to draw the conclusion, and people are more reluctant to give up a conclusion that they themselves have drawn.

Identifying Faulty Enthymemes

When someone makes a bad argument in the form of an enthymeme, it may be difficult to spot the error because the error is often in the unstated premise.  Therefore, it is to our great advantage to learn to identify enthymemes and supply the missing premise.  When the missing premise is absurd, we need to graciously point this out.  Ask yourself these two questions: (1) What additional premise is needed to make this argument valid? (2) Is that premise reasonable?  A masterful example of this occurred during the Bahnsen-Tabash debate.

The Christian apologist Dr. Greg Bahnsen participated in a formal debate against the atheist lawyer Edward Tabash on the topic of the existence of God.  Tabash’s opening statement consisted essentially of a tirade of complaints about how evil God is in Tabash’s opinion, and how much Tabash doesn’t like God or what God does.  His conclusion was that God does not exist.  In his rebuttal, Dr. Bahnsen pointed out that Tabash’s dislike for God is logically irrelevant to the question of God’s existence, unless we supply the missing premise “whatever Tabash does not like must not exist.”  But that premise is absurd!  When we flesh out Tabash’s enthymeme in its full form, the absurdity becomes clear:

  1. Whatever Tabash does not like does not exist (major premise, unstated by Tabash)
  2. God is something Tabash does not like. (minor premise – explicitly stated)
  3. Therefore, God does not exist. (conclusion)

The first premise is clearly ridiculous.  Things do not cease to exist simply on the basis that a person doesn’t like those things.  And yet, without that premise, there is no logical way to conclude “Therefore, God does not exist” from the premise “Tabash does not like God.”  In the first 30 seconds of his rebuttal, Dr. Bahnsen had exposed his opponent’s entire argument as utterly absurd.  Clearly, the ability to identify and refute the unstated proposition in an enthymeme is a useful skill in apologetics.

Consider the enthymemes often used in origins debates.  Evolutionists frequently point to similarity in the traits and anatomy of animals as evidence of a common ancestor.  The argument is something like this: “Virtually all animals have certain structural traits in common.  Therefore, they are (likely) biologically descended from a common ancestor.”  When we supply the missing premise, the absurdity of the argument is exposed:

  1. Those things which have structural traits in common are (likely) biologically descended from a common ancestor.
  2. Virtually all animals have structural traits in common.
  3. Therefore, virtually all animals are (likely) biologically descended from a common ancestor.

The first premise was originally unstated, but it is clearly absurd since counter-examples are abundant.  Virtually all cars have structural traits in common (wheels, doors, an engine, etc.); does this mean they are likely biologically descended from a common ancestor?  Clearly not.  Cars have structural similarities because such structures are necessary for the function of the car.  Furthermore, two cars may be especially similar if they had the same creator – if they were produced by the same company.

Evolutionists sometimes argue on the basis of similarities in DNA.  “All organisms use basically the same genetic code in their DNA; a given base pair codon codes for the same amino acid across virtually all life.  Therefore, all organisms have evolved from a common ancestor.”  The stated premise is basically true.[1]  But in order for the argument to valid, the missing premise must be: “Whatever uses the same code must be descended from a common ancestor.”  But all English articles use the same code: English.  The words mean the same thing regardless of what article they are in.  Therefore, if the first premise were true, we would have to conclude that all articles have descended from a common ancestor.

Another common example is “Of course Darwinian evolution is true.  The majority of scientists believe it.”  The conclusion is stated first: “Darwinian evolution is true.”  The supporting premise is “the majority of scientists believe [Darwinian evolution].”  What additional premise must be supplied for the argument to be valid?  When fleshed out, the argument becomes:

  1. Whatever the majority of scientists believe in is true.
  2. The majority of scientists believe in Darwinian evolution.
  3. Therefore, Darwinian evolution is true.

The first premise was unstated in the original enthymeme.  And sure enough, it is absurd.  History is replete with claims now known to be false but which were accepted by the majority of scientists of the time (such as a geocentric solar system).

Unfortunately, creationists are not immune from making fallacious enthymemes.  A creationist once wrote that natural selection “is not really real” because (he argued) it has a misleading label.  Of course, the premise that the label “natural selection” is misleading is debatable, but let’s suppose for the sake of argument that it is indeed misleading.  What premise would have to be supplied to make the argument valid? The full argument with the major premise explicitly stated would be the following:

  1. That which has a misleading label is not really real. (This is the unstated premise.)
  2. Natural selection has a misleading label.
  3. Therefore, natural selection is not really real.

Of course, when fleshed out, the absurdity becomes clear.  Who in their right mind would accept the first premise: that real things cannot have a misleading label?  Are we to believe that Rhode Island is not really real on the basis that it is not a literal island?  Peanuts are not really nuts; they are legumes.  So can we conclude that they are “not really real?”  If I name my white dog “Blacky” will he suddenly cease to exist?  Is there some cosmic force that prevents human beings from assigning a misleading label to a real object or phenomenon?

Labels are ultimately arbitrary.  In many cases, we may choose a label that is descriptive of its referent, but this is not a requirement.  Sometimes people intentionally label something in a misleading way, perhaps for the sake of humor.  As a graduate student I occasionally used a computer programming language called “ANA”, an acronym which stands for “A Non Acronym.”  Of course, that humorously misleading label did not cause the programming language to cease to be real!

Don’t be Fooled

Bad arguments abound.  And it is far too easy to be bluffed into a false conclusion by a good presenter using a fallacious enthymeme, or some other logical fallacy.[2]  How many people have been intimidated into accepting a faulty conclusion espoused by a confident buffoon?  We have a moral obligation to reason rationally both in our internal thinking and when attempting to persuade others.  And that means examining arguments carefully and always in light of Scripture (Acts 17:11).

When presented with an argument, first ask, “Does the conclusion follow from the stated premises?”  If not, then the argument may be an enthymeme.  And if it is an enthymeme, we then analyze whether it is a reasonable one by filling in the argument.  Ask, “What additional premise must be supplied in order for the conclusion to follow from the other premise(s)?”  When the additional premise is supplied, all that remains is to ask, “is that premise reasonable?”  You may be surprised at how often it is not.




[1] There are a few exceptions.  In some categories of organisms, a particular base pair codon will code for a different amino acid (or a stop codon) than in others.  But the majority of codons are the same across organisms.

[2] Of course, there are many types of fallacious arguments.  My book Discerning Truth covers the most common fallacies.