When is Maybe the Right Answer?


Another concept that will help you make sense of current events (and everything else) is the difference between deductive and inductive reasoning.


Deductive Arguments


Arguments that are deductive contain everything needed to evaluate an argument within the premises and conclusion of the argument itself. For example, if I told you that voting in a particular state’s Democratic primary required you to be a registered Democrat, you could evaluate the following argument without knowing anything else:


Premise 1: In this state, you must be a registered Democrat to vote in the Democratic primary.

Premise 2: Jules voted in this state’s Democratic primary.


Conclusion: When Jules voted in the primary, he was a registered Democrat.


Concepts of validity and soundness introduced here and utilized here, here and here apply to deductive arguments. If you recall, a valid argument is one in which accepting the premises requires you to accept the conclusion. In the case of the argument above, there is no way to accept the premises and reject the conclusion (by coming up with a counterexample in which the premises are true, but the conclusion false, for example).


Therefore, the argument is valid. And if the premises are true, then this valid argument is also sound.


Inductive Arguments


Inductive arguments are less airtight than deductive ones. For example, suppose Jules has a twin sister Julia for whom this argument applies:


Premise 1: Julia has voted Republican in every election since she turned 18.

Premise 2: Julia has been wearing a MAGA hat every day since Donald Trump became President.


Conclusion: Julia will vote for Trump in next year’s election.


In this case, it is easy to come up with scenarios in which the premises are all true, but the conclusion false.


For example, if the impeachment process currently underway ends up with Donald Trump being removed from office, that means Julia would not have the opportunity to vote for him in next year’s presidential election (although I suppose she could still write him in). Julia might also change her mind about whom to vote for between now and election day. Perhaps she’ll end up preferring whomever the Democrats nominate, or maybe she will end up voting for a third-party candidate whose policies align more closely with her beliefs. Julia might also forget to vote, or her car might break down on the way to the polling station.


While all of these alternatives are possible, they are very unlikely given what we know about Julia’s voting history and what’s implied by her choice of headgear. This means that our argument’s conclusion is very likely, but not certain, to be true, given the premises.


This is why inductive arguments are described as strong or weak, rather than valid and invalid, based on the strength of the inferences leading from premises to conclusion. The strength of the logic connecting an argument’s premises to its conclusion is often based on probability, rather than the all-or-nothing standard of validity used in deductive reasoning.


Deduce or Induce?


You might be tempted to think that deductive arguments are inherently superior to inductive ones, given that certainty seems preferable to likelihood based on probability. But keep in mind two names associated with perfected thinking, both of whom relied primarily on inductive vs. deductive reasoning: Sherlock Holmes and Albert Einstein.


Readers of Arthur Conan Doyle’s stories may be familiar with the Holmes quote: “Once you eliminate the impossible, whatever remains, no matter how improbably, must be the truth.” This quote describes an inductive process in which an argument is constructed from known facts (such as observations of a crime scene) to inform a conclusion most likely to be true.


As for Albert Einstein, like Sherlock Holmes – and like all scientists – his thinking process was based on drawing likely conclusions based on known facts and observations. This means that science – which may represent humankind’s most successful and productive form of reasoning – is primarily inductive vs. deductive.


Given that the tools you are learning about on this site are designed to help you navigate the news of the day, let’s use them next time to determine whether anyone should be considered too young (or too old) to run for President.

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