Logical fallacies

by scotslawstudent

Logic is very important to law. Depending on who you ask it’s all there is to law. A problem that lawyers have is that they have somewhat given up the advantage of surprise the moment they say they’re a lawyer – I don’t know how effective emotive pleas are if they come from someone you know is being paid to say it regardless of their personal feelings. I think it takes the shine off it slightly. That leaves you with logical argument to persuade people with.

There are a lot of other areas where logic is also extremely important. Causation in science is probably the biggest example in normal life. Homoeopathy is getting a lot of attention lately as the low-hanging fruit of implausible alternative therapies and a lot is being made of the niggling issue that bruises which go away may not go away because of the infinitesimally small amount of water in which arsenic was dissolved but then diluted away you drank. The sceptic community is very vocal about people who use this sort of thing as proof that homoeopathy can cure everything.

“I feel it worked for me, therefore it works for everyone” is not good logic, it’s technically called “inductive logic” which is generally fine as long as you question your presumptions (eg, that it actually did work for you) and don’t rely on it too much. Of course, if your entire argument is extrapolating a major premise from a minor premise, stop and get a new argument. It probably won’t stand up very well. You can get away with it if no one challenges it but the problem with legal disputes is that someone generally does.

Theskepticguide.org have compiled a list of 20 of the most common logical fallacies that they experience. It’s really worth using them as cautionary tales so that you don’t end up getting stuck with an argument that cannot withstand scrutiny.

Ad hominem

An ad hominem argument is any that attempts to counter anothers claims or conclusions by attacking the person, rather than addressing the argument itself. True believers will often commit this fallacy by countering the arguments of skeptics by stating that skeptics are closed minded. Skeptics, on the other hand, may fall into the trap of dismissing the claims of UFO believers, for example, by stating that people who believe in UFO’s are crazy or stupid.

This is very common in normal life and I’ve fallen for this one myself – it’s very tempting to spend your time as a respondent proving that a claimant is a bad person who deserved what happens to them when actually what you need to do is look at what you’re required to prove under applicable law.

Slippery Slope

This logical fallacy is the argument that a position is not consistent or tenable because accepting the position means that the extreme of the position must also be accepted. But moderate positions do not necessarily lead down the slippery slope to the extreme.

Although this is a logical fallacy it is a perfectly acceptable policy argument. It is often within a court’s discretion to consider policy arguments, but I wouldn’t feel comfortable actually relying on it to any great extent just because it’s so vulnerable to questions like “yeah, but what if we don’t immediately go out and kill all the children?”. There’s a lot you can say in an essay that a court might do that a court might never actually do.


tautology is an argument that utilizes circular reasoning, which means that the conclusion is also its own premise. The structure of such arguments is A=B therefore A=B, although the premise and conclusion might be formulated differently so it is not immediately apparent as such. For example, saying that therapeutic touch works because it manipulates the life force is a tautology because the definition of therapeutic touch is the alleged manipulation (without touching) of the life force.

I actually really disagree with this one, I think what they mean to say here is just “circular argument”. If you really can base your argument on a tautology you’re actually on excellent logical ground. A tautology is something that is necessarily true. A circular argument is terrible, unhelpful to you and should always be avoided but if you rely on something that logically has to be true (or the universe doesn’t work) you’re not going to be wrong about it. For example “an armed robber is a robber who has a weapon” is a tautology, which means that if you can prove (to the standard of proof) the two points of 1) he was a robber and 2) he had a weapon he must be an armed robber, if you’re prosecuting him for armed robbery this is exactly what you’re there to prove. I find it really helps me to work out what legal issues are at question if I actively try, as much as possible, to reduce all logical questions to tautologies.

Tu quoque

Literally, you too. This is an attempt to justify wrong action because someone else also does it. “My evidence may be invalid, but so is yours.”

As far as I’m concerned as a bright eyed, idealistic LLB student who sees the world in strictly black and white this is the worst thing ever. It turns out, surprisingly, that bad things can happen to bad people. There’s simply no good reason why someone who did something wrong shouldn’t be able to get legal remedy for wrongs done to them.

This is why, for example, Napier v Scottish Ministers was right to grant Article 3 relief to a prisoner who was held in inhuman conditions even though he was in jail (if I recall correctly he was even awaiting trial at that point – merely accused). There’s no good reason to breach the human rights of people held in jail. It doesn’t work to say “well, they’re bad so you can be bad to them.” That just doesn’t follow – it’s a tu quoque fallacy.

Unstated Major Premise

This fallacy occurs when one makes an argument which assumes a premise which is not explicitly stated. For example, arguing that we should label food products with their cholesterol content because Americans have high cholesterol assumes that: 1) cholesterol in food causes high serum cholesterol; 2) labeling will reduce consumption of cholesterol; and 3) that having a high serum cholesterol is unhealthy. This fallacy is also sometimes called begging the question.

This is an important one – it’s so important to challenge your own presumptions when you’re looking at any legal problem. I think the best example I ever had was a time I was (too) casually reading a hypothetical scenario and I assumed the guy did it and actually he hadn’t. As you might guess this had an effect on what my answer ended up being. Law school essays get around this, through IRAC, by very much encouraging you to spell everything out.

They have a much longer list at the above link that’s worth checking out.

But, on a personal note, the big one that annoys me more for reading comprehension reasons than any logical issues is:

Begging the question

(So annoying I’ve mentioned it twice)

This does not mean you need to immediately state the question that you think needs asked. When it says “beg” it doesn’t actually ask for the question, it just means someone is assuming a principle. It means that the other person hasn’t asked a question they should have asked, not that you need to suggest one.

“That begs the question – what colour is my bike?” is a pet peeve of mine. It just means that someone assumes your bike is yellow when they should investigate their foundational principles. It doesn’t mean you should tell them they should ask you what colour your bike is. Just say either “you’re begging the question there” or “you need to ask [x]” but avoid saying both.

H/T to Crispian Jago.

You might also want to check out the gripping blog of Diane Levin who every month, like clockwork, debunks a logical fallacy. I’ve covered it on the blog before and it’s excellent.