This post was first published on CoderHood as Famous Quotes, and Other Logical Fallacies. CoderHood is a blog dedicated to the human dimension of software engineering.
Logical fallacies and their ugly heads
Logical fallacies will show their ugly head in dialog during your career in tech, and life in general. Do not let that go! It will distort reality and introduce contradictions to supposedly logical arguments. People regularly repeat phrases and quotes as unquestionable truths, because some famous person said them in the past. Such phrases sound smart and are attached to famous names that we would not dare to question. People repeat those phrases because we are used to them, and we assume them to be true.
An example of "famous" quote containing logical fallacies
An article I recently read reminded of a quote by Sir Arthur Conan Doyle, which has a logical fallacy:
"Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."
When you hear someone quote this monstrosity, don't let it go! It is a logical fallacy, and it is simply wrong. Just because Arthur Conan Doyle was a "Sir" and wrote books about a smart detective, it does not mean he was right all the time.
This phrase is like saying the following:
"Once you eliminate all disgusting foods, whatever remains must be delicious."
Clearly, that is not the case! If you had 10 foods in front of you, and you eliminate the ones that you consider "disgusting", some remaining foods would be good, some just edible, and some delicious.
Additionally, similarly to "truth" and "impossible," what is "disgusting," "just edible," "good," and "delicious" are also subject to interpretation, muddying the matter even more.
Once you eliminate the impossible, what remains is "not impossible," which simply means "possible." If something is possible it does not mean that it is true, nor likely. It simply means that there is a non-zero chance of it being true, not a certainty.
Logically correct statements, sometimes don't sound as smart as similar fallacies
Sir Arthur Conan Doyle should have stated the principle as follows:
"Once you eliminate everything that is not the truth, whatever remains, no matter how improbable, must be the truth."
See the difference? Let's brush aside --- for a moment --- the fact that "truth" is often subjective and thus subject to interpretation, and let's say that we have an unquestionable or at least self-consistent concept of truth. "Not the truth" and "truth" are logical opposites, so the quote starts making more logical sense. Written this way, however, it doesn't have the same punch and frankly seems obvious.
Many similar logical fallacies are regularly quoted, and they mostly stem from the fact that people fail to state negatives of statements. Despite what we might teach kids, the opposite of "always" is not "never." The opposite of "always" is "not always," which is different from "never."
Conclusion
Question everything, even if you heard it before, some famous person said it, and "sounds" smart.
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Top comments (2)
I think you don't have to take it literally .. Of course it's wrong. It mean that the thing you through impossible, IS possible.
Do not say something is impossible if you're not sure.
Days before, I was using apache + php and one extension was uncommented but.. still show as not loaded.
I tried to change PHP version, same thing. I was like "It's impossible ! DLL is present, line is uncommented, I've restarted my server..".
There was a missing dll in apache folder.. Once I eliminate the impossible, whatever remains, no matter how improbable, was the truth.
Words are important. This quote has been used time and time again literally. When you hear it used to make a point, run! You could decide to explain it with personal interpretations, but if you do that words lose their meaning.
BTW, Sir Arthur Conan Doyle meant it literally, like everything else Sherlock Holmes did, and it is often used literally.