Science: Logical fallacies Part 1

Logical fallacies have less to do with science and more to do with logic. Logic itself is a massive subject and one that can take a lifetime to master. Thankfully today we’ll only be covering a small section of logic. There are generally around 30 logical fallacies, although sometimes they can get broken down into more for clarity. To keep things simple I’m going to limit us to 5 fallacies at a time, otherwise these posts could end up being very long indeed.

Fallacies are categories of fallacious thinking. In a nutshell this means constructing an argument based on poor reasoning. Honestly this definition is pretty harsh. The reason logical fallacies are so important to understand in regards to science is because we all make them, and far more often than you might think. As you’ll see, some fallacies could even be linked to the shortcuts our brains take, which is often an evolutionary advantage despite being illogical. Getting past some of these is extremely difficult, as they’re practically hardwired into us. However, if we wish to uncover the truths of our world it is important we understand these fallacies, as they can be quite crippling to furthering our understanding.

Before we dive into the actual fallacies, lets briefly cover a little logic 101.


All arguments follow a certain structure. An example of this might be:

Premise 1: A = B.

Premise 2: B = C.

Conclusion: Therefore A must also = C.

A more tangible example of this might be:

Premise 1: Cows are mammals

Premise 2: All mammals are warm-blooded

Conclusion: Therefore cows are warm-blooded.

This is all very basic right here, but at the end of the day most arguments boil down to something very similar. Now for an argument to be believed it needs to be both ‘sound’ and ‘valid’. But what does it mean to be both sound and valid?

A valid argument is one in which the premises follow, as with the example above. An example of an invalid argument might be:

Premise 1: Cows are mammals

Premise 2: All reptiles are cold-blooded.

Premise 3: A cow is not a reptile.

Conclusion: Therefore a cow must be warm-blooded.

The problem with this argument is that although all reptiles are cold-blooded, that doesn’t immediately mean everything that isn’t a reptile is warm-blooded. What’s particularly interesting about this argument is that although it is not valid, the conclusion is still true. Just because an argument is invalid or unsound doesn’t immediately make the conclusion false. It just means it’s not true for the reasons the arguer is putting forth.

A sound argument is one in which the premises are true. An argument can be valid (everything follows), but unsound (the premises are untrue). An example of this might be:

Premise 1: Cows are reptiles.

Premise 2: All reptiles are cold-blooded.

Conclusion: Cows are cold-blooded.

As you can see here, the logic is valid. If cows were reptiles and reptiles were cold-blooded, then cows would be cold-blooded. But as I’m sure you know, cows aren’t reptiles. This argument is valid, but not sound.

The final example is that of an argument that is sound, but not valid. These probably won’t come up as often as they’re easier to spot, but for consistencies we’ll cover it.

Premise 1: Cows are mammals.

Premise 2: Lizards are reptiles.

Conclusion: Cows eat grass.

All these statements are true (sound) but the conclusion doesn’t follow from the premises.

The one final thing worth mentioning in this logic 101 course, is that of assumptions. There are many gaps in our knowledge. In some cases we have a pretty good idea of what is likely, although we don’t know for certain. Using these ideas as premises can be dangerous, because if our assumptions are wrong then the argument may suddenly become invalid or unsound without our realising it. Where possible, try to avoid assumptions in arguments. That said, it is perfectly acceptable to use assumptions, it’s just fair to let the person you’re debating with know it’s an assumption. If they have a different assumption you may find yourselves with different conclusions and not understand why.


So let’s take a look at a couple of starter fallacies.

Ad hominem

Ad hominem is Latin for “to the man”. This is where someone chooses to attack the arguer, rather than the argument. The idea is that if you discredit the arguer people will no longer listen to their point of view. Unfortunately this can be quite effective, but we should recognise it for the logical fallacy it is.

An example might be: “He’s just a Bible thumping Creationist; he doesn’t know anything about evolution.”

Of course the flip is equally true: “She’s an atheist, so she doesn’t get why religion is important to people.”

Although it might be true that ‘he’ doesn’t know anything about evolution nor ‘she’ about religion, it’s not true because of the first premise. For clarity, let’s break it down into our logic 101 system.

Premise 1: He’s a Bible thumping Creationist.

Premise 2: Creationists know nothing about evolution.

Conclusion: He knows nothing about evolution.

Hopefully you can see that ad hominem fallacies are valid, but unsound. That is, the premises logically follow, but premise 2 is not true.

Argument from personal incredulity (AKA: Argument from ignorance)

This is one of my personal favourites, because I see it coming up so frequently. Basically this argument amounts to:

X happens.

Y appear to be the only explanation.

Therefore Y is the answer.

Going back to our logic 101, this is an example of an invalid argument (doesn’t follow), however, it doesn’t immediately mean the conclusion is false. The conclusion very well may be true, but not for the reason the arguer is presenting.

This is also stepping into assumption territory. The arguer is assuming that Y is the correct answer, while other people may not make that assumption.

The reason this type of argument is fallacious is because the arguer may simple not be aware of other explanations. Just because you can’t imagine an alternative explanation doesn’t mean the one you have is correct.

Two of the most common examples of this type of fallacy I’ve seen are:

Premise 1: The universe is incredibly complicated.

Premise 2: Only an incredibly intelligent agent could create something so complicated.

Premise 3: God is an incredibly complicated agent.

Conclusion: God created the universe.

Premise 2 is our issue here (although there’s another fallacy hidden in Premise 3). It is a big assumption to conclude only intelligence can create complexity. Not only do we have counter examples of this, but there’s a whole universe of undiscovered things out there that could provide an alternative answer.

The other is most commonly used to explain UFO sightings:

Premise 1: I saw some strange lights in the sky.

Premise 2: Alien spacecrafts make strange lights in the sky.

Conclusion: I saw an alien spacecraft.

It may be true that alien spacecrafts could make lights in the sky. Our spacecraft do, so why not theirs? The assumption here is of course that these lights are in fact of alien origins and not our spacecraft. Oftentimes people who claim to have spotted UFOs say they moved in very strange ways. Ways that would be impossible for anything humans have created to move.

But that too is an assumption. Isn’t it at least possible (in this writers opinion, more likely) that the military happen to have made something that can move in very complicated ways that the sighter simply isn’t aware of?

Okay guys, this post is now over 1,000 words, so rather than tackling another 3 fallacies I’m going to leave it there. If you’re new to the ideas of valid and sound arguments this will no doubt be plenty for you to think about. In the next post I’ll pick up where we left off with another 5 or so fallacies.