How to win an argument (Part 3)

In part 1 we had a look at four problems of reasoning, stemming from generalisations and implications:

1. Destroying the exception - all swans are white... until you find a black one.
2. Disregarding the exception - all surgeons are criminals cos they cut people up.
3. Mistaking the direction of the arrow (confirming the consequent) - clouds mean it must be raining.
4. Mistaking the meaning of the arrow (denying the antecedent) - no rain means there must be no clouds.

In part 2 we saw how distractions, intended or not, can come in many forms and begging the question is something journalists constantly get wrong:

1. Red Herrings - arguments that don’t address the issue.
2. Straw Men - arguments that address a superficially similar, but in fact different issue.
3. Loaded Questions - controversially complex questions that presume things that haven’t been proved.
4. Begging the Question - when the conclusion is assumed in the argument.

In this third part, we’ll look at laziness of thinking, particularly to do with cause and effect. This will lead us to a discussion of similar mistakes with words rather than reasoning.

In the next and final part, we’ll have a look at some real arguments and take them apart.

It’s worth noting at this stage that, while we’re looking at all these fallacies as ways to break down your opponent’s arguments, they should also be a guide for you to develop your own indestructible arguments.


-- Flying Penguins

Non sequitur is Latin for ‘doesn’t follow’. All logical fallacies can be described as non sequitur, but it is predominantly used to mean an argument where the conclusion doesn’t follow from the premises. This might be because the argument is invalid (we’ve been looking at ways in which this might be the case), or because it is not sound.

I should explain that difference:

Valid means:
If the premises are true, then the conclusion is true.

Invalid means:
If the premises are true, that doesn’t mean the conclusion is true (it could be true, but that would just be a coincidence).

Sound means:
A valid argument with true premises (and so a true conclusion).

Unsound means:
A valid argument with at least one false premise OR an invalid argument.

A valid and sound argument:
All men are mortal.
Ben is a man.
Therefore, Ben is mortal.

A valid but unsound argument:
All animals with wings can fly.
Penguins have wings.
Therefore, penguins can fly.

This is unsound because the first premise is false.
It is valid because, if the first premise was true, the conclusion would be as well.

An invalid (and so unsound) argument:
All men are mortal.
Jane is mortal.
Therefore, Jane is a man.

Can you spot why this argument is invalid? If you can, then you’re doing well. (Clue: Clouds.)

So the two ways an argument can be non sequitur (conclusion doesn’t follow from the premises) is either by being invalid or unsound.

There are lots of ways this can happen, but I want to look particularly at our laziness of thought when it comes to causation. Previously, we looked at mistakes that come from reasoning based on generalisations and the problem of inductive reasoning (going from specific instances to a universal generalisation). Inductive reasoning was not called that when Hume was discussing it. [Don’t know who Hume is? See Swans.] He talked about causal reasoning and was concerned with what it means for one thing to cause another. This is intricately linked with making generalisations (induction), but I won’t bore you with how (if you want to find out, check out this introduction - a little technical, but readable).


-- Farting Dogs

So what does it mean for one thing to cause another? Well, a major part of it must be that the effect comes after the cause and not the other way round. However, we need to be a bit more specific than that, because me turning on the TV just before the dog farts does not mean that the remote controls the dog. For one thing to cause another, it must always do so in the same conditions. This way, my pressing the power button on the remote causes the TV to turn on (if the batteries aren’t dead), but doesn’t cause the dog to let loose.

When one thing always follows another thing, they are said to be in ‘constant conjunction’. Hume was worried; he thought there was nothing more we could say about cause and effect. He was worried because, for example, day and night are in constant conjunction - but day does not cause night, nor the other way round. It’s these kinds of difficulties that make up our next batch of logical fallacies.

If two things always occur together, we feel like they must be linked in some way. Birds start singing in the morning, just before the sun rises - does birdsong cause the sun to rise? What about if your child develops autism after he’s been vaccinated - did the vaccination cause the autism? I’ve got a new flatmate and ever since she arrived the boiler has been playing up - does her presence cause the boiler’s problems?

Be careful! When we feel like there is a connection between things, we tend to misjudge how strong it is and can easily be swayed into believing the connection goes one way when it doesn’t. This mistake comes up a lot more often than you’d think.

Another way of making this mistake is to look at events that happen to occur at the same time and conclude that one causes the other. This is usually because there is a less obvious thing that causes them both. Let’s say I notice that, in the UK, people wear less clothing during the summer months. I want to know why. They also consume much more ice cream. I conclude that the increased consumption of ice cream is causing people to shed their winter-wear and jump into skimpy swimwear. Whoops.

These causal misunderstandings (not ‘casual misunderstandings’ as I keep writing) can be very subtle. For example, we saw in part 1 how we can easily feel that rain and clouds have a deeper relationship than they actually do. When they are subtle, they are difficult to spot.


-- Non-existent Sofas

Another pair of mistakes that are related to this generalisation/induction misunderstanding are when we say something is true of the whole because it is true of some part, or vice versa.

“The university is seven hundred years old, therefore all the staff are seven hundred years old.”

“Every band member of Heaven’s Nails is brilliant, therefore Heaven’s Nails are brilliant.”

The first argument makes the mistake of saying that the whole has a property, so its parts must do too.
The second argument mistakes individual brilliance for band cohesion. It may be that they work really badly together, regardless of how brilliant they are individually.

Some more examples:

“This tiny piece of tin foil cannot be torn by hitting it with a hammer, therefore the spaceship I have made by wrapping large sheets of tin foil around a thin wooden frame is impervious to hammers.”

“Atoms are 99.9 per cent nothing. My sofa is made of atoms. Therefore, 99.9 per cent of my sofa doesn’t exist.”

Keep your eyes peeled...


-- End of Part 3

This time we’ve seen the most common of argument mistakes: non sequitur - what they claim simply doesn’t follow from what they have said. There were a few specific examples:

1. Two things happen in succession - this doesn’t mean the first caused the second.
2. Two things happen around the same time - this doesn’t mean they are linked.
3. The parts aren’t necessarily the same as the whole.
4. The whole isn’t necessarily the same as its parts.

Next time:
We’ll deconstruct some real arguments from Debatewise.org.