If you want to discern the truth behind mainstream news reporting, "fake news," conspiracy theories, and alternative media, you need to be able to recognize the difference between sound reasoning and unsound reasoning. The use of flawed reasoning does not necessarily invalidate a conclusion, but it does call that conclusion into question. An astute media consumer can use a few simple logical tools to check how reliable a media report is even before pursuing an in-depth independent investigation.

Post hoc, ergo propter hoc

This Latin phrase roughly translates to, "After this, therefore because of this." The sequence of events does not prove a causal relationship between those events. This form of argument appears persuasive because it assumes there is a causal relationship, and the audience for this argument is often biased to agree with it.

Historians and economists all too often use this line of reasoning to justify policy prescriptions for political action, basing there arguments on "X happened, then Y, so we need to implement policy A so B will occur." The assumed causal relationship may not exist, or may be tenuous at best with influence from numerous other factors. The second event may not in fact be a necessary consequence of the first.

Cum hoc, ergo propter hoc

Similar to the above, this roughly translates from Latin to "With this, therefore because of this." Both post hoc and cum hoc can be considered examples of the correlation/causation fallacy but they are subtly different. Post hoc refers to a sequence of events, while cum hoc refers to simultaneous occurrences.

For example, if I were to argue that the relaxation of restrictions on firearm carry over the past 30 years and the massive decrease in violent crime over that same period were linked, it would not be a valid argument in and of itself. Both initial facts are true, but there may not be an actual causal relationship between them. Would it be valid to use this argument to prove that firearms need to be entirely unregulated and decriminalized? No. With the addition of further data and reasoning, such an argument could be made. However, on its own, this is not an argument.

Rodin's The Thinker, image via Wikipedia

Confirmation Bias

This is the most difficult problem in any rational discussion. No one is immune. Politicians, economists, theologians, scientists, historians, and anyone else seeking an answer to a question must try to avoid this tendency to seek evidence to support their preconceptions and disregard as erroneous any contradictory arguments. Both sides of the climate change debate accus ethe other of such bias, for example.

"You want to find evidence of climate change to support your political agenda and ensure a steady government-funded job!"

"Oh yeah? Well, YOU are just a shill for Big Oil out to excuse pollution of the environment with no concern for the future!"

And so on ad nausium.

Straw Man

This is a deceptive form of argument where instead of directly addressing an opponent's statement, a caricature is created to be attacked instead. This is commonly encountered by advocates of liberty.

"You don't like taxes? But taxes pay for essential services the government provides! You don't want us to have roads, security, fire prevention, education, etc. and so on!"

The liberty advocate is thus portrayed in opposition to those services, regardless of any evidence and reasoning he uses. The caricature is far easier to attack than the real arguments presented.

Image via Apologia

Ad Hominem

Another Latin phrase, this time meaning "Against the man," indicates an argument directed at an opponent personally rather than against his statements. There are many subtypes of this fallacy, and it belongs to a larger category of fallacies known as "fallacies of irrelevance."

Anyone who has had a discussion about race and gender issues has likely encountered something like, "You're wrong because you're a cis white male!" Similarly, discussions about past US presidents might end with something like, "If you disagree with my interpretation of Obama's legacy, you're a racist!"

Now, it is possible that my interpretation of events may be colored (pun intended) by my gender, cultural background, sexual orientation, and skin color to the point where it could affect my argument, but a unsupported accusation to avoid my actual argument is a dishonest evasion.

There is a distinction to be made here, though. Some arguments get heated, and heated responses are not necessarily fallacious.

"You are wrong because you're an asshole!" - ad hominem

"You are wrong, here's why, and you're an asshole!" - not ad hominem

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This is by no means exhaustive, and there are many sites dedicated to describing various fallacies and explaining their patterns along with how to recognize them. Some of my favorites:

yourlogicalfallacyis.com
nizkor.org
fallacyfiles.org
wikipedia.com