Mental Model: Deductive vs Inductive
To argue well it is not only important to know your facts but also to understand the flow of logic and the structure of the argument.
Two of the most common arguments types are deductive and inductive arguments.
By the end of this piece, you’ll know how to categorise arguments into these 2 buckets and possibly become a better, more rational debater.
Structure of the Arguments
Deductive arguments start with a general principle and based on that we infer a specific proposition.
For example:
Rick always wears a white coat in the lab. (General principle)
Rick will be in the lab on Thursday.
Rick will be wearing a white coat on Thursday. (Specific proposition)
We go from knowing that Rick always wears a white coat in the lab to inferring that if he is in the lab on Thursday then he should be wearing a white coat that day.
Inductive arguments on the other hand start with specific propositions and based on that we infer a general principle.
For example:
Rick wore a lab coat to work on Monday. (Specific proposition)
Rick wore a lab coat to work on Tuesday. (Specific proposition)
Rick wore a lab coat to work on Wednesday. (Specific proposition)
Therefore, Rick always wears a lab coat to work. (General principle)
Here we establish a pattern of sorts by making specific observations on Monday, Tuesday and Wednesday (past behaviour) and infer by the extension of that logic that Rick always wears a lab coat to work.
Strength of the Conclusion
A key differentiating feature of these 2 argument types is the strength of the conclusion a.k.a level of certainty.
Deductive Argument Conclusions
In a deductive argument, if all the premises are true, the conclusion must be true.
Rick always wears a white coat in the lab. (True)
Rick will be in the lab on Thursday. (True)
Rick will be wearing a white coat on Thursday. (True)
However, if the conclusion is not true then one of the general principles must be false.
Rick always wears a white coat in the lab. (False)
Rick will be in the lab on Thursday. (True)
Rick will be wearing a white coat on Thursday. (False)
This makes deductive arguments very strong. So in order to convince someone with a deductive argument, you just need to prove that your premise is true and the conclusion will take care of itself.
Burning plastic causes air pollution (Premise 1)
Breathing polluted air is bad for asthma patients (Premise 2)
If you establish the fact that Burning plastic do indeed cause air pollution and that breathing polluted air is bad for asthma patients, then you have a water tight argument that “Burning plastic is bad for asthma patients”.
To counter a deductive argument, your goal should to be attack the validity of the premise.
There is no other way to win other than to invalidate/disprove one or more premises.
Inductive Argument Conclusions
On the other hand, with an Inductive argument, even if all the premises are true the conclusion might still be false.
Rick wore a lab coat to work on Monday. (Specific proposition) - True
Rick wore a lab coat to work on Tuesday. (Specific proposition) - True
Rick wore a lab coat to work on Wednesday. (Specific proposition) - True
Therefore, Rick always wears lab coat to work. (General principle) - True/False
Since we are making assumptions about the propositions outside of our 3 premises in the example above, we can never really be sure about the certainty of the conclusion.
While Monday, Tuesday and Wednesday are being accounted for, we are still missing information about Thursday and Friday. While it is likely that Rick could wear a lab coat on Thursday and Friday based on past behaviour, it is not certain by any means because we do not have that information.
The conclusions to inductive arguments are only probabilistic in nature and never certain.
This is not to say that inductive arguments are bad arguments, but rather that it should not be considered with certainty.
In a good inductive argument, the likelihood of the conclusion being true is high and in a bad inductive argument, that likelihood is low.
You can counter an inductive argument by presenting evidence of inconsistency in the data not included in the premise.
Example:
Politician A was corrupt
Politician B was corrupt
Therefore, all politicians are corrupt
You can counter the above by comparing the sample size (2 politicians) to the actual number of politicians (thousands) and point out the insignificance of the sample size.
You can also try to prove one of the premises in the argument wrong. If you can prove that Politician B is not corrupt, you’ll make an already weak argument completely false.
Knowing these 2 types of arguments can help you spot logical inconsistencies and think more rationally.
So that’s it. What are your thoughts on this post? Let me know by replying to this email.
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