• 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