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.

If you enjoyed this article, keep in touch!

• Find all my posts on CoderHood.
• Join my professional network on LinkedIn.
• Follow me on Twitter.
• Join my Facebook page.
• And finally, follow me here on dev.to!