• Argument by Analogy

    I have often said that I hate argument by analogy.  What I really mean is that I hate argument by false analogy.

    An argument by analogy can be useful, provided that the things being compared are actually analogous.  Let’s consider an example.

    I have driven several Ford vehicles and didn’t like any of them.  For my next vehicle, I’m not going to shop at Ford dealerships because I won’t like anything they have.

    I think that this is a fair argument.  Vehicles from one manufacturer are highly analogous.  Many use the same parts, even though the design is different.

    DNA is like a ladder made of different colored macaroni.*

    DNA may look like a twisted ladder, when represented in a very basic form.  However, this is a false analogy.  DNA is not anything like macaroni (colored or not). And it’s really not much like a ladder either, when you actually start looking closely at it.

    One thing about arguments from analogy is that conclusions drawn from them are not logically necessary.  The conclusions may be valid and they MAY present good evidence for the conclusion.  But it’s not a case of if A=B and B=C, then A=C.  It’s much more like A=B and both have characteristics x, y, and z.  Therefore, if A has character r, then it is possible (even likely) that B also has character r.

    A false analogy results when they two things being compared are not that similar or have some fundamental differences.  For example, one of the most common things you’ll hear from creationists is this analogy.

    • A watch is highly complex and has a designer
    • A living thing is highly complex
    • Therefore, a living thing has a designer

    The problem here is that there is a fundamental difference between a watch and a living thing.  Living things are capable of self-reproduction and will often have mutations that result in differences from the parent organism.  In this, there is a false analogy.  Because watches and living things are so very different, a comparison between the two cannot be valid.

    It doesn’t matter, for the purposes of the analogy, whether living things have a designer or not.  The analogy is still false and is still an invalid argument.

    That’s what a lot of people don’t get.  An argument can still be invalid/false/incorrect even if what is being argued is true.  It’s a common mistake that a lot of people make.

    That’s why I don’t like argument by analogy.  It’s so easy to falsify.  All one has to do is point out how the analogy is not valid.  A counter-example is usually sufficient.

    Analogies have a useful place in teaching and in thinking.  I use analogies all the time in teaching because it’s possible to relate information that is unknown to information that is known in this way.  However, I always make it known that this is an analogy and may not be a perfect representation of the system.

    People who are knowledgeable about a subject can make arguments without depending on argument by analogy.  If one wants to argue about DNA, then argue about DNA, don’t argue about how macaroni doesn’t do something and then say that one’s argument about DNA is correct.



    *  I actually had a student present this ‘hypothesis’ for a science fair.

    Category: PhilosophyScienceSkepticism


    Article by: Smilodon's Retreat

    • Analogies are best as a prompt for continued active reflection on the respects in which they hold or don’t hold.

      BTW, does the watch really have “a maker”? One agent who fully preconceived its design and was then able to follow all of the steps necessary in its production? Or was it rather the distributed product of many minds, organized by various mechanisms which are no more minds than is evolution by natural selection (e.g., market forces, social conventions, governments)? Maybe the right way to use the analogy is in reverse:

      “Suppose you come you come across a rabbit. Obviously, no one mind could have completely overseen its creation…rather, you know that it required some kind of feedback process operating over deep time. Now, suppose you come across a Prius. Is it not just as obvious that distributed and impersonal systems, developed over a long time, were crucial to its creation?”

      • SmilodonsRetreat

        When William Paley presented the watchmaker argument in 1802, there was probably a single watchmaker… with the provision that the watchmaker didn’t actually invent the watch itself and was only constructing it from plans or knowledge acquired from others.

        As far as the rabbit, there’s some truth to what you say and to a reasonable person, I would be willing to use that version. But creationists are nothing if not unreasonable. Goddidit and since he’s perfect/omnipotent/omniscient/etc he can do anything.

        Once, I asked a creationist why organisms’ bodies had major design flaws. His response was that God can’t create anything with a design flaw. By definition, whatever God creates is perfect. It us who just thinks that it isn’t perfect. The mind boggles…

    • Ben MacLaren

      By “false analogy” you mean a bad analogy. Clearly the analogy has to be well-chosen.

      Some properties in the source of the analogy transfer, and others don’t. The more salient they are, or the more people commonly associate those properties with the source, the better the analogy. When deeper/richer properties are being transferred (e.g., proportional or causal relationships), rather than superficial attributes (e.g., color, size, weight). Invariant properties are more likely to be transferred than properties that frequently change. Also, if the “student” is unfamiliar with the source, it is a bad analogy.

      Saying “DNA is like a ladder” is not inherently a worthless analogy (for someone who knows nothing about DNA, but a lot about ladders), but adding “made of macaroni” (especially “different colored macaroni”) adds nothing, so it weakens the analogy.

      It is absurd to say DNA is not like computer code, or a blueprint. You just can’t push the analogy further than it makes sense, or use it with people who know more about biology than computers. The Rutherford model of the atom was better than the plum pudding model, because it accounted for the fact that most alpha waves easily passed through them. Your justification for claiming DNA isn’t like computer code is “like” saying the Rutherford model wasn’t valid because electrons don’t have a diameter of 8,000 miles.

      Don’t throw the baby out with the bath water. Don’t throw out the analogy between DNA and computer code because some idiot is trying to use the analogy to argue that any other properties of a computer apply to DNA, like it must have have been designed by an intelligent being. Refining the analogy to maximize its benefit for a particular audience is fine. Don’t try to insist it is bullet-proof to idiots who will try to misuse it.