Today’s S3 Core Lesson

  1. Using the videos on the blog tagged ‘core’, find those examples on your sheet and, with a partner, try to work out what is wrong with the logic. Just in your own words. Record this on your sheet.
  2. Using the excellent site below, read the descriptions of the various fallacies and try to work out which is/are committed in each example. Be ready to justify your answer to the class.screen-shot-2016-09-19-at-10-29-12
  3. This is quite hard. If you get finished, try to think of a strategy to make it easier. Put another way, why do people come up with such different answers in this task? What could you do to solve this?



The Revolution will be televised..

Great for testing your critical thinking skills:

So It’s a well known fact that if we got rid of the Queen, within a couple of years we’d be a communist state led by anarchists led by Ken Livingston.

Look at the French, they got rid of the Monarchy and they’re a bunch of Ar***oles. Do we want to be like the French?

We’ve got not not actual evidence that she is a witch, but then again we have no actual evidence that she is not a witch.

If you ask yourself why has The Sun witch-hunts against paedophiles, Muslims and Gypsies but never against actual witches? conspiracy theory?

family guy again…

In ‘Screwed the Pooch’ Brian is up in courst and the prosecution lawyer cross examines Peter…

Lawyer: Mr Griffin, which of the following two phrases best describes Brian Griffin: Problem Drinker or African-American Haberdasher?
Peter: Uh, do I-I guess problem drinker, but that’s uh-
Lawyer: Thank-you. Now: Sexual deviant or magic picture that if you stare at it long enough, you see something?
Peter: Well, sexual deviant, but that other one’s not even, eh-
Lawyer: Thank-you

post hoc ergo propter hoc

Good news!! some more Latin for you to learn. This is a fairly simple idea that is so common sense and so everyday life that it shouldn’t be hard. What’s wrong with superstition, witch hunting and the ‘God Channel’?

We all know, from life as well as other bits of philosophy, that (almost) everything that happens has a cause. And that’s fine. And that’s what scientists look at and use to do all the amazing things they do. But it’s a bit more complicated: Sometimes things can look like causes when in fact they aren’t at all…

Sometimes something looks like it happened because of something else when in fact it just happened after something else….

What if you’re watching something happen; say a tap in the kitchen is dripping. In fact it started right there when you sat down to watch a film. You could leave it, but the noise is spoiling your viewing experience, so you decide to sort it.

To stop it, you obviously need to find the cause. And having just a little bit of common sense you know that causes come before effects and that you should think about what you did before the dripping started.

So you made a drink, took your popcorn out the microwave, and sat on the sofa. But you don’t know which has caused the dripping. Now you know that that microwave and the sofa probably have nothing to do with the tap, so you go and check you turned off the tap properly and that’s it – problem solved.

Unfortunately in life we don’t always know the one (or more) thing(s) that causes something. And that’s why scientists use controls and ‘fair tests’ and things like that to find the events that are actually causes and not things that just coincidentally happen before… And that brings us to what these words mean…

If you met someone who thought that turning on Christmas lights made it snow you might have reason to question their intelligence. But why? What if this person has seen, with their own eyes, the snow start thirty times in a row when the Christmas lights are switched on?

Well of course it could mean that they have witnessed a magic switch, but it’s much more likely a coincidence. Just because it has snowed just after the switch, with some frequency, does not mean that there is a causal (causing) link between the two.

Now why this matters for arguments in philosophy… Quite often a person making an argument will say that they did something and that made something else happen…. But what if it didn’t…

Post hoc ergo propter hoc literally means ‘after this, therefore because of this’.

Post hoc ergo propter hoc literally means ‘after this, therefore because of this’. And when you say it like that it makes sense that philosophers have a problem with this sort of reasoning. Obviously lots of things do happen because of things that happen before, but that doesn’t mean that everything that happens before is the cause of what follows.

Peg Tittle talks of a friend who asked for a raise at her work. The company was doing very well and had taken on new staff so her friend looked at the company’s performance stats and went into the office saying “since I have started here the sales have doubled, I deserve a raise”. This makes a a little more sense in standard form:


fallacy of equivocation

kerosine is fuel…

red bull is fuel…

therefore kerosine is red bull…

This might seem like a fairly obvious mistake… and the reason it’s funny here is  due to this – but the same error is found (arguably) at the centre of a number of complicated and high level philosophical arguments… Let’s have a look…

Leibniz’s Law – Identity of Indiscernibles

What’s this?

This is the North Pole.

No, it’s not. Yes, it is.

No, it’s not. Yes, it is.

No, it isn’t. Yes, it is.

No, it isn’t. Yes, it is.

No, it’s not. Where’s the snow?

The Identity of Indiscernibles is a principle of analytic ontology first explicitly formulated by Wilhelm Gottfried Leibniz in his Discourse on Metaphysics, Section 9 (Loemker 1969: 308). It states that no two distinct things exactly resemble each other. This is often referred to as ‘Leibniz’s Law’ and is typically understood to mean that no two objects have exactly the same properties. The Identity of Indiscernibles is of interest because it raises questions about the factors which individuate qualitatively identical objects. Recent work on the interpretation of quantum mechanics suggests that the principle fails in the quantum domain (see French 2006). [from SEP]

Reductio ad absurdum – finally an example….

Last night when I was out I ended up sitting across from a massive group of girls who were preening themselves and clucking like something out of an episode of family guy. It was like our city’s version of TOWIE.

Anyway as the night went on one girl calls her ‘mate’ an unrepeatable word alluding to her friend’s ‘unattractiveness’. The friend was clearly hurt by this remark and quickly pointed out that she had been brought several drinks this evening and that the girl with the extensive vocabulary had been unapproached all night.

to this the original girl said something meaning something like ‘yes dear, but that’s because I’m so stunning that everyone one in this establishment is intimidated by me…’. One of her other friends chuckled. The original insulted girl muttered under her breath that that would mean she must be the most attractive girl in the club – perhaps even the city. The implication was clear, even though it passed the person at whom it was directed uncomprehended. the whisperer was stating something that she thought was obviously ridiculous.

And this is it. This is what philosophers are doing when they use the word absurd.

The Day After Tomorrow

- What are you doing?

- What did you think we would burn?

- You can't burn books.

- No, absolutely not.

You want to freeze to death?

I'll go get some more.

I'll help you.

I'm going with them.

Okay, do you have a cafeteria or a lunchroom?

Just an employees' lounge with a few vending machines.

We're not gonna last long on M&M's and potato chips.

What about the garbage cans?

There's always something to eat in the garbage.
Friedrich Nietzsche?
We can't burn Nietzsche.

He was the most important thinker of the 19th century.

Please. He was a chauvinist pig in love with his sister.

He was not a chauvinist pig.

But he was in love with his sister.

Excuse me? You guys?

Yeah, there's a whole section on tax law down here that we can burn.


Welcome errors in reasoning. This site is designed to help students of philosophy at all levels understand how philosophical arguments work (and don’t work) in greater detail. It is designed to be useful for those studying the Critical Thinking section of Higher and Intermediate 2 Philosophy as well as those lucky enough to be reading the International Baccalaureate syllabus.

Most sites of this nature are no better than textbooks on logic, but with this blog I will endeavour to provide ‘real’ examples of all the technical terms coined. Arguments are one of the least abstract applications of philosophy in real life. Everywhere you look people are trying to convince you of things, whether it’s what to buy or who to believe. We will try and expose the basic errors in reasoning regarded by many as common sense.