.jpg)
Think It Through: the Clearer Thinking Podcast
Think It Through: the Clearer Thinking Podcast
Episode 23: Hey Sherlock, Why Is Deductive Reasoning So Difficult?
In this episode, April can't decide whether to pronounce "deductive" as "DEE-duk-tiv" or "de-DUK-tive," so she just switches back and forth between them to see if anyone notices.
Episode 23 Show Notes:
Why Sherlock Holmes is more an inductive than a deductive kind of guy:
http://philsci-archive.pitt.edu/5306/1/Holmes.pdf
Some good basic information about deductive reasoning:
https://www.criticalthinking.com/articles/induction-vs.-deduction
http://www2.fairmontstate.edu/users/ffidura/cogpsy/cpthnkng.html
https://www.livescience.com/21569-deduction-vs-induction.html
https://examples.yourdictionary.com/deductive-reasoning-examples.html
Jesse Martin’s LinkedIn blogpost about the importance of deductive reasoning:
https://www.linkedin.com/pulse/science-learning-deductive-reasoning-jesse-martin
My evidence (for the example syllogism) that Japanese has a homogeneous population and everyone there speaks Japanese:
My support for the claim (in my other example) that not all people who are in favor of public health options are socialists:
https://morningconsult.com/2021/03/24/medicare-for-all-public-option-polling/
Job websites recognize the necessity for good deductive reasoning skills in the workplace:
https://www.indeed.com/career-advice/career-development/improve-deductive-reasoning-skills
https://www.indeed.com/career-advice/career-development/deductive-skills
https://www.glassdoor.com/blog/guide/deductive-reasoning/
The research that shows most of us can do deductive reasoning:
https://digest.bps.org.uk/2008/12/11/sudoku-puzzles-show-were-all-capable-of-deductive-reasoning/
What’s going on in your brain when you do puzzles? Read these:
https://www.psychologytoday.com/us/blog/brain-workout/200904/puzzles-and-the-brain
https://www.rd.com/article/what-happens-to-your-brain-when-do-a-puzzle/
Some fun/frustrating logic puzzles:
Episode 23: Why is Deductive Reasoning so Difficult, Sherlock?
Hello and welcome to episode 23 of Think it Through.
My critical thinking students just finished their chapters on deductive reasoning, and as usual, a certain number of them understood the concepts being discussed; however, the majority of them had a lot of difficulty with things like the difference between modus tollens and modus ponens, and how categorical claims can be illustrated by Venn diagrams, and you’re probably already thinking “What the hell is she talking about, and why should I care?” Which is very likely what many of my students were thinking while trying to figure this stuff out. I absolutely understand that frustration.
Let me just say that I am NOT a philosophy professor, I’m a communication professor. Most of the students in my class are either communication or journalism majors, and they want to be news reporters or writers or something along those lines. The learning outcomes of my class are to look at everyday forms of persuasion and argumentation and apply good critical thinking skills to those things to help make sense of them, to look at the evidence provided to see if it’s reasonable and holds up to scrutiny, and to see the ways some persuaders use fallacious reasoning or manipulation to further their own ends, and especially to help my students understand that good critical thinking and good ethical choices go hand in hand; both are involved in news reporting and writing, or they certainly should be. You don’t need a doctorate in philosophy to realize that, but you do need to have a basic understanding of the ways that we come to conclusions, and deductive reasoning is one of those ways. But it can be a difficult thing to understand, and in today’s episode, we’re going to find out why that is, and what we can do about it. Let’s get started…
MUSIC
Of course you’ve heard of Sherlock Holmes, the character created by Sir Arthur Conan Doyle in 1887 who is the prototype for every subsequent mastermind detective. He has long been assumed to be a brilliant master of deduction, which might be one reason why people assume that deductive reasoning is so difficult—apparently only geniuses can do it! But let’s put that myth to rest right now. There are some reasons why it’s difficult for us to think deductively, but not having a genius level IQ isn’t one of them. Frankly, the main reason thinking deductively is so difficult is because it doesn’t come naturally to us. Jesse Martin, professor of psychology at the University of Leithbridge in Alberta, refers to deductive reasoning as a higher-order thinking skill that doesn’t really start developing until adolescence; and by that time we’ve already had years of thinking inductively (which is why that kind of reasoning is easier for us). He also says that studies in the 1960’s and 70’s found that only about 40% of adults could use deductive reasoning well, and even more disheartening, recent studies have shown that number has decreased to as low as 20%! Here’s the thing; it’s not that people don’t WANT to think deductively, but they may have never been taught to think that way. So if we think of it at all, we think of it as this mysterious way of divining truth, and we assume that only really smart people like Sherlock Holmes are capable of understanding it.
Although really, did Sherlock Holmes solve all his cases just by using deductive reasoning? Well, he certainly did use it, but he was also just as likely to use inductive reasoning when solving a case. Remember, inductive reasoning is reasoning by example. We gather enough evidence to show that something is probably or likely the case, and if we do it correctly and don’t fall victim to any inductive fallacies like we talked about in the last episode, it’s very likely that we are correct. Sherlock Holmes’ character was portrayed as a brilliant master of observation; he would come to a correct conclusion by gathering evidence quickly and accurately, unlike the other characters around him. In fact, he often chided his sidekick Dr Watson by saying that Watson saw everything, but didn’t really process what he was looking at, and that’s how most of us go through life. Now, we might not be as observant as Sherlock Holmes, but we are certainly capable of inductive reasoning, and if we do it correctly, we have a decent chance that our conclusion will be accurate. This is not to say our conclusion is absolutely 100% correct, because inductive reasoning isn’t meant to be precise, only that the conclusion is probably or likely to be correct. We are also capable of revising our initial conclusion if we find more evidence that leads us in another direction, but that’s one of the things that inductive reasoning allows for.
Deductive reasoning, on the other hand, is very structured and precise and doesn’t allow for possibilities, only certainties. Unlike induction, which starts with examples or instances of something and uses that information to generate a likely conclusion, deduction starts with a known fact or a general truth and applies it to an example or an instance of something related to it to see if a conclusion can be drawn about that thing. This kind of reasoning often uses a specific form called a syllogism. There are different types of syllogisms, but one of the most common consists of a major premise (that’s the known fact or general truth), a minor premise (that’s the specific instance or example we are applying the major premise to), and a conclusion that we draw when we put those two things together. We use deductive reasoning in math all the time; here’s a simple example:
All numbers ending in 5 are divisible by 5. The number 45 ends with a five. Therefore, 45 is divisible by 5.
So we take the known mathematical fact that all numbers ending in 5 are divisible by 5, and we apply it to one specific number, the number 45. Based on that, we can determine that because 45 ends in 5, it is divisible by 5. Unlike inductive reasoning, this conclusion is not probably correct; it’s definitely correct.
The thing about deductive reasoning is that in order to be a valid argument the syllogism must be structurally correct. As I said, there are a couple of different types of valid, or structurally correct, deductive reasoning patterns, and while I don’t have time to get into what they are, I’ve put some resources in the show notes so if you’re interested you can explore further. Good deductive arguments must be both valid (structured correctly) and sound, which means that both the premises are true. If it is both valid and sound, then the conclusion MUST be true. So for that math problem we can see that each of those premises was true, and it was structured correctly, so we can be certain that the conclusion is also true.
Now, for each one of those valid deductive structures there is an invalid type based on a mistake in the structure of the argument; these are called formal fallacies. So one of the things that makes deductive reasoning difficult may be that we think we’re doing it right, but we’ve committed one of those formal fallacies. Here’s an example of a valid deductive structure: If a, then b. a, therefore b. Let’s apply that to something in real life, so maybe “If people are born and raised in Japan (that’s a), then they speak Japanese (that’s b). Kiko was born and raised in Japan (that’s the specific example of a), so she speaks Japanese (that’s b, the conclusion we reach).” Now, as awkward as that sounds, and we probably wouldn’t actually say something like that in a conversation, it’s still a valid deductive argument in that it is structured correctly, and as long as both those premises are true, the conclusion must also be true--if indeed she was born and raised in Japan, she speaks Japanese. And yes, I looked it up; 99 percent of the population speaks Japanese as their first language, and those that speak mainly in another language, if they were born and raised in Japan, they are still expected to know and speak Japanese. But anyway, I digress, back to the argument. The conclusion that Kiko speaks Japanese because she was born and raised in Japan is true based on the general fact that people born and raised in Japan all speak Japanese. So this argument is both valid and sound.
But it’s very easy to commit a formal fallacy with this same information by switching it up a bit and saying something like, If people are born and raised in japan, they speak Japanese; Kiko speaks Japanese, so she was born and raised in Japan. Now, you might be thinking, well that’s true too. Actually, even though both of those premises are still correct, the conclusion that she was born and raised in Japan isn’t necessarily true. She might have been, but it’s just as likely that she was born and raised in California and either spoke Japanese at home or learned it in school. But simply speaking Japanese doesn’t mean someone was born in Japan, even though being born and raised in Japan pretty much guarantees that you speak Japanese. This second argument is invalid because it’s not structured in a way that makes the conclusion necessarily true. So in deductive reasoning, structure is critical to whether the argument is a good one or not, and if you don’t understand that concept, then you won’t understand deductive reasoning.
Music
Still confused? Yeah you can see what I mean when I say that deductive reasoning is difficult.
Another reason it’s hard is that we often leave out parts of deductive arguments because they are, as I said before, often awkward and hard to verbalize. We can also leave parts out because we have already assumed those parts to be true and figure everyone else does too, so why bother saying them? Like, in real life you might be talking with another person and they mention that your friend Kiko speaks Japanese fluently, and you say something like, “well, after all she WAS born and raised in Japan.” You’ve left out parts of the argument, but the other person will automatically fill in the blanks and figure out what you meant. Syllogisms with parts missing are called enthymemes, and while it seems like they should make our reasoning somewhat easier they could also contribute to reasoning errors, either because the structure is incorrect or we are assuming the truth of one of our premises that might not actually be true.
Here's an example: Maybe you’re arguing with someone about a political candidate and you say she’s a socialist because she is in favor of government-run health care. Your argument is an enthymeme, but if you were to put it into a full syllogism it would be: Socialists favor government-run healthcare. This candidate favors government-run health care. Therefore, this candidate is a socialist. Now, you might feel like that’s a good argument but it’s not, it’s a formal fallacy because it’s structured incorrectly. Plus it’s not necessarily true; There are plenty of reasons someone might favor government-run healthcare that wouldn’t make them a socialist. A recent poll by Morning Consult found that 7 out of 10 Americans favor a public health insurance option, including 56% of Republicans surveyed, and I’m sure those people would take great offense at being called socialists. So, the argument that the candidate is a socialist because she favors government run healthcare—yeah, if that’s your argument, your argument sucks.
Music
Like Sherlock Holmes, scientists use both inductive and deductive reasoning when they employ the scientific method. Inductive reasoning tends to be used to form a hypothesis (by observing something over time and noting that there are enough instances of it happening out there in the world that it might just be the case generally). Deductive reasoning is used in the scientific method to test that hypothesis by applying it to a specific situation to see if it indeed holds up. A scientist says, “Ok if my hypothesis is correct, then here is what I should observe in this experiment.” And the research process goes back and forth from induction to deduction until finally the researchers have results that they are sure reflects reality accurately. But once those results are published, the general public may have a lot of difficulty following the reasoning behind the results, and the conclusions that were drawn from those results. It’s certainly easier for some people to figure out than others; understanding deductive reasoning is directly linked to one’s educational attainment; the more education you’ve received, the more likely it is that you’ve at least learned what deductive reasoning is. However, just like any other skill, you have to practice it to get better at it. But most of us don’t, and even if we do have a clue about what it is, that knowledge alone may not be enough to help us make decisions about important issues that affect our lives. Here’s what Professor Martin says about the problems that arise from lack of good deductive reasoning skills, and I quote:
“Why does this matter? Because there is a growing chasm between the scientific world and society in general. Most of the members of our society are cognitively unable to follow the arguments scientists use to demonstrate what they are finding, and scientists can’t understand why the members of our society just don’t look at the evidence and come to the same, obvious conclusions that they have. The lack of deductive reasoning means that members of society are simply unable to follow the logic, and so must turn to other sources to find out the truth…The lack of ability to engage in deductive reasoning for a majority of participants in a Western Democracy is problematic, to say the least. Unable to reason and follow logical arguments means that up to 80% of adults must turn to a trusted source in order to determine what they think about any issue that hangs on deductive reasoning. These trusted sources with their own agendas can influence large swathes of the population and move public opinion and policy making in their own desired direction.” End quote
Now, Martin doesn’t mean to imply that all trusted sources have evil hidden agendas; in episode 19 I mentioned the kinds of sources that we could trust to translate complicated scientific findings for us, like science writers, journalists who specialize in science, and the scientists themselves, IF they are also good at communicating information to the general public. But instead of just relying on these people all the time, we really need to start caring about our own ability to think deductively. If poor deductive reasoning skills are a problem, then what can we do to improve those skills?
The job search website Indeed gives pretty good career advice to job seekers, and they recognize that good deductive reasoning skills can help improve job performance. They also understand that developing these skills takes time and practice. Their advice includes general tips like, always be curious and observant, keep learning new skills, listen to podcasts, read books, try to stay up-to-date on industry trends. Break problems down into their component parts to see if you can spot why a problem occurred and how it might be fixed.
A good way to improve your deductive skills is to look at some of the ideas and concepts that you think are “fact,” which are the claims you would use as the major premises in many of your deductive syllogisms. Look at those statements and see if you can explain why you think they are facts. Do some research, using good, credible, unbiased sources, to make sure those beliefs actually have some basis in reality, and aren’t just things you’ve assumed to be the case. Practice identifying the logic behind your decisions.
One of my favorite ways to practice deductive reasoning skills is to play Sudoku. It’s deductive reasoning in its purest form, and it’s something that anyone can learn with practice. In a 2008 experiment, researcher Louis Lee had people who were unfamiliar with Sudoku play it, just telling them the rules but not giving them any strategies and letting them figure it out for themselves. While most of them were only able to solve a portion of the puzzle, they had no trouble adequately explaining their deductive reasoning for the answers they did find. This showed that we can certainly make deductions about abstract concepts, so it’s not completely foreign to us. I recommend downloading a Sudoku app onto your smartphone and playing it at least once a day. Start with easy games, and work your way up. It’s kind of addicting, and there’s something very satisfying about finishing one of those puzzles.
Logic problems are also a good way to exercise your deductive thinking muscles. These are sometimes fun, sometimes frustrating, but even if you get them wrong, it’s good to look at the answer to find out where your logic went south. They can be as simple as a few sentences with a question to answer, or as complicated as a story that uses a grid and a series of clues to help you to identify contradictions and eliminate possibilities to finally arrive at a solution. I’m not quite as good at these puzzles as I am at Sudoku, but I like to challenge my brain this way, so I do them regularly. I’ll post some links to logic problems that you can do online in the show notes.
While games like this might not give you an understanding of deep truths about the world, they do some very helpful things to your brain that can make deductive reasoning easier, according to Marcel Danesi, the author of The Total Brain Workout:
· For one thing, Puzzles engage us in a “mental hunt” for something, so in that way we are doing something similar to a detective or a scientist, engaging in a “quest for understanding”
· And, when we are trying to complete a difficult game like a crossword or Sudoku, we are activating areas of our brain that we don’t normally use, which can only be a good thing. In fact, puzzles activate both the left and right hemispheres of the brain.
· As I said before, it’s very satisfying when you finish a puzzle. That’s because you get a rush of dopamine in the area of your brain responsible for rewards and reinforcement.
· And, while the jury is still out on this one, certain types of puzzles may improve cognitive function and help prevent the loss of brain power in older adults. I’m really hoping that one turns out to be the case.
Music
As I said at the beginning of the episode, my students often struggle with deductive reasoning; it’s entirely possible that my college-level class is the first time they’ve ever had to focus specifically on thinking deductively. I can give them the basics, but without continual practice those particular thinking muscles aren’t going to improve. As I send them on their way at the end of the semester, all I can do is hope that they’ve been motivated to keep working on their deductive reasoning skills. And I’d like to think I’ve done the same for you! Until next time, I hope you use this information to help you think it through.