If you're conducting research on a topic, you'll use various strategies and methods to gather information and come to a conclusion.
Two of those methods are inductive and deductive reasoning.
So what's the difference between inductive and deductive reasoning, when should you use each method, and is one better than the other?
We'll answer those questions and give you some examples of both types of reasoning in this article.
What is Inductive Reasoning?
The method behind inductive reasoning
When you're using inductive reasoning to conduct research, you're basing your conclusions off your observations. You gather information - from talking to people, reading old newspapers, observing people, animals, or objects in their natural habitat, and so on.
Inductive reasoning helps you take these observations and form them into a theory. So you're starting with some more specific information (what you've seen/heard) and you're using it to form a more general theory about the way things are.
What does the inductive reasoning process look like?
You can think of this process as a reverse funnel – starting with more specifics and getting broader as you reach your conclusions (theory).
Some people like to think of it as a "bottom up" approach (meaning you're starting at the bottom with the info and are going up to the top where the theory forms).
Here's an example of an inductive argument:
Observation (premise): My Welsh Corgis were incredibly stubborn and independent (specific observation of behavior).
Observation (premise): My neighbor's Corgis are the same way (another specific observation of behavior).
Theory: All Welsh Corgis are incredibly stubborn and independent (general statement about the behavior of Corgis).
As you can see, I'm basing my theory on my observations of the behavior of a number of Corgis. Since I only have a small amount of data, my conclusion or theory will be quite weak.
If I was able to observe the behavior of 1000 Corgis (omg that would be amazing), my conclusion would be stronger – but still not certain. Because what if 10 of them were extremely well-behaved and obedient? Or what if the 1001st Corgi was?
So, as you can see, I can make a general statement about Corgis being stubborn, but I can't say that ALL of them are.
What can you conclude with inductive reasoning?
As I just discussed, one of the main things to know about inductive reasoning is that any conclusions you make from inductive research will not be 100% certain or confirmed.
Let's talk about the language we use to describe inductive arguments and conclusions. You can have a strong argument (if your premise(s) are true, meaning your conclusion is probably true). And that argument becomes cogent if the conclusion ends up being true.
Still, even if the premises of your argument are true, and that means that your conclusion is probably true, or likely true, or true much of the time – it's not certain.
And – weirdly enough – your conclusion can still be false even if all your premises are true (my Corgis were stubborn, my neighbor's corgis were stubborn, perhaps a friend's Corgis and the Queen of England's Corgis were stubborn...but that doesn't guarantee that all Corgis are stubborn).
How to make your inductive arguments stronger
If you want to make sure your inductive arguments are as strong as possible, there are a couple things you can do.
First of all, make sure you have a large data set to work with. The larger your sample size, the stronger (and more certain/conclusive) your results will be. Again, thousands of Corgis are better than four (I mean, always, amiright?).
Second, make sure you're taking a random and representative sample of the population you're studying. So, for example, don't just study Corgi puppies (cute as they may be). Or show Corgis (theoretically they're better trained). You'd want to make sure you looked at Corgis from all walks of life and of all ages.
If you want to dig deeper into inductive reasoning, look into the three different types – generalization, analogy, and causal inference. You can also look into the two main methods of inductive reasoning, enumerative and eliminative. But those things are a bit out of the scope of this beginner's guide. :)
What is Deductive Reasoning?
The method behind deductive reasoning
In order to use deductive reasoning, you have to have a theory to begin with. So inductive reasoning usually comes before deductive in your research process.
Once you have a theory, you'll want to test it to see if it's valid and your conclusions are sound. You do this by performing experiments and testing your theory, narrowing down your ideas as the results come in. You perform these tests until only valid conclusions remain.
What does the deductive reasoning process look like?
You can think of this as a proper funnel – you start with the broad open top end of the funnel and get more specific and narrower as you conduct your deductive research.
Some people like to think of this as a "top down" approach (meaning you're starting at the top with your theory, and are working your way down to the bottom/specifics). I think it helps to think of this as "reductive" reasoning – you're reducing your theories and hypotheses down into certain conclusions.
Here's an example of a deductive argument:
We'll use a classic example of deductive reasoning here – because I used to study Greek Archaeology, history, and language:
Theory: All men are mortal
Premise: Socrates is a man
Conclusion: Therefore, Socrates is mortal
As you can see here, we start off with a general theory – that all men are mortal. (This is assuming you don't believe in elves, fairies, and other beings...)
Then we make an observation (develop a premise) about a particular example of our data set (Socrates). That is, we say that he is a man, which we can establish as a fact.
Finally, because Socrates is a man, and based on our theory, we conclude that Socrates is therefore mortal (since all men are mortal, and he's a man).
You'll notice that deductive reasoning relies less on information that could be biased or uncertain. It uses facts to prove the theory you're trying to prove. If any of your facts lead to false premises, then the conclusion is invalid. And you start the process over.
What can you conclude with deductive reasoning?
Deductive reasoning gives you a certain and conclusive answer to your original question or theory. A deductive argument is only valid if the premises are true. And the arguments are sound when the conclusion, following those valid arguments, is true.
To me, this sounds a bit more like the scientific method. You have a theory, test that theory, and then confirm it with conclusive/valid results.
To boil it all down, in deductive reasoning:
"If all premises are true, the terms are clear, and the rules of deductive logic are followed, then the conclusion reached is necessarily true." (Source)
So Does Sherlock Holmes Use Inductive or Deductive Reasoning?
Sherlock Holmes is famous for using his deductive reasoning to solve crimes. But really, he mostly uses inductive reasoning. Now that we've gone through what inductive and deductive reasoning are, we can see why this is the case.
Let's say Sherlock Holmes is called in to work a case where a woman was found dead in her bed, under the covers, and appeared to be sleeping peacefully. There are no footprints in the carpet, no obvious forced entry, and no immediately apparent signs of struggle, injury, and so on.
Sherlock observes all this as he looks in, and then enters the room. He walks around the crime scene making observations and taking notes. He might talk to anyone who lives with her, her neighbors, or others who might have information that could help him out.
Then, once he has all the info he needs, he'll come to a conclusion about how the woman died.
That pretty clearly sounds like an inductive reasoning process to me.
Now you might say - what if Sherlock found the "smoking gun" so to speak? Perhaps this makes his arguments and process seem more deductive.
But still, remember how he gets to his conclusions: starting with observations and evidence, processing that evidence to come up with a hypothesis, and then forming a theory (however strong/true-seeming) about what happened.
How to Use Inductive and Deductive Reasoning Together
As you might be able to tell, researchers rarely just use one of these methods in isolation. So it's not that deductive reasoning is better than inductive reasoning, or vice versa – they work best when used in tandem.
Often times, research will begin inductively. The researcher will make their observations, take notes, and come up with a theory that they want to test.
Then, they'll come up with ways to definitively test that theory. They'll perform their tests, sort through the results, and deductively come to a sure conclusion.
So if you ever hear someone say "I deduce that x happened", they better make sure they're working from facts and not just observations. :)
TL;DR: Inductive vs Deductive Reasoning – What are the Main Differences?
Inductive reasoning:
- Based on observations, conversations, stuff you've read
- Starts with information/evidence and works towards a broader theory
- Arguments can be strong and cogent, but never valid or sound (that is, certain)
- Premises can all be true, but conclusion doesn't have to be true
Deductive reasoning:
- Based on testing a theory, narrowing down the results, and ending with a conclusion
- Starts with a broader theory and works towards certain conclusion
- Arguments can be valid/invalid or sound/unsound, because they're based on facts
- If premises are true, conclusion has to be true
And here's a cool and helpful chart if you're a visual learner:
That's about it!
Now, if you need to conduct some research, you should have a better idea of where to start – and where to go from there.
Just remember that induction is all about observing, hypothesizing, and forming a theory. Deducing is all about taking that (or any) theory, boiling it down, and testing until a certain conclusion(s) is all that remains.
Happy reasoning!