Faulty logic: Post hoc, ergo propter hoc

For the next in the series on faulty logic, we have:

Post hoc, ergo propter hoc

It’s a natural tendency for people to make connections between events. “When I do this, that happens.”

When I touch something hot, I get burned.
When I don’t water my house plants, they die.
When I eat that kind of mushroom, I get sick. … continue reading this entry.

How to feel like a non-expert? Get your taxes done.


At first, tax preparation would seem to have nothing to add to skepticism, but bear with me. Anyone who knows me well knows the issue that gets me going, and I don’t get up on my editorial soap-box very often, but… the three greatest challenges to being a good skeptic are obtaining, judging and understanding information. That is why we have experts. … continue reading this entry.

Faulty logic: Appeal to Popularity

It’s been too long since I’ve written an installment of the series on faulty logic. It’s time to continue it, with…

Appeal to Popularity

There was a time when pretty much everyone thought that the Earth was flat. There was a time when anyone who thought about it was sure the sun went around the Earth. Come to mention it, there was a time when that was widely attributed to its having a ride on Apollo’s chariot. These were popular ideas.

But an idea’s popularity doesn’t make it right; it only makes it popular. … continue reading this entry.

Faulty logic: Appeal to Authority

Continuing the series on faulty logic, today we’ll look at:

Appeal to Authority

In our society, we hold various people up as authority figures, those we’re inclined to pay attention to. It’s not always clear why we have some folks on that list, really. Political leaders, such as presidents, prime ministers, kings, queens, senators, and governors are obvious. Educators and other academics — professors, scientists, and the like — also make sense. I’m never sure why actors and sports figures are there, but they do seem to be. … continue reading this entry.

Faulty logic: False Dichotomy

It’s time for number two in a series of posts on faulty logic. Today’s fallacy:

False Dichotomy

We like things to be black or white, tall or short, here or there. We like to consider two sides to every story.

Unfortunately, there aren’t always two sides. Sometimes there’s only one; more often, there are multitudes. Many facets on the stone. Nooks and crannies in abundance. Things are usually not either black or white, but multicolored. As it’s hard to argue a case with so many variations, we tend to narrow the scope, and argue one side against another.

The trouble comes because we tend to define the two sides in a lopsided manner, revealing our biases and mischaracterizing one side or the other. If you’re not “pro-life”, what are you? Anti-life? Of course not: it’s a false dichotomy. … continue reading this entry.

Faulty logic: Confirmation Bias

In “On being a skeptic”, I said that skeptics look at evidence and make rational judgments based on the evidence:

We don’t say, “Bullshit!”, and we don’t say, “It’s a scientist saying it, so it must be true.” We look at the evidence.

Even the most hardened skeptic is susceptible to confirmation bias. We might think, “that traffic light is always red,” even when we know it is programmed to change at regular intervals.I note that non-skeptics — or those who style themselves as a different kind of skeptic — also put forth “evidence” and claim support from it. But their evidence turns out to be faulty, and, often, the fault is in their reliance on one of more logical fallacies. They’re using faulty logic, which is generating faulty evidence, which is supporting… not any judgment they might make from what they see, but what they’ve already determined they want to believe.

I thought I’d have a look, in a series of posts, at some of the common logical fallacies. I’ll start with the one that’s perhaps the hardest for us to avoid, one that most of us have to work hard not to fall into ourselves.

Confirmation Bias

Simply put, confirmation bias is seeing what you want or expect to see, and ignoring what contradicts it. … continue reading this entry.

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