Logic and Fallacies: thinking clearly

In this interactive session we explore some basic principles of philosophy, we dissect different kinds of fallacious reasoning and show how these techniques are often used to trip up Christians in conversation. This session should teach you to begin thinking around issues and problems as they come in the form of different questions and statements.


It is important to be able to recognise statements and questions which are internally fallacious. If you don’t realise this and so jump in with an answer, you can become confused and fall into traps which could easily be avoided.

  • Fallacious reasoning, once detected, can often be dealt with by asking the questioner a clarifying question in turn.
  • If we learn to recognise how people think, we can then engage with them more effectively.

Fallacies of Ambiguity

Phrasing or punctuating the same set of words in different ways can produce entirely different meanings:

Dear John,

I want a man who knows what love is all about. You are generous, kind, thoughtful. People who are not like you admit to being useless and inferior. You have ruined me for other men. I yearn for you. I have no feelings whatsoever when we're apart. I can be forever happy – will you let me be yours?



Dear John,

I want a man who knows what love is. All about you are generous, kind, thoughtful people, who are not like you. Admit to being useless and inferior. You have ruined me. For other men, I yearn. For you, I have no feelings whatsoever. When we're apart, I can be forever happy. Will you let me be?

  • Some statements can be read in two ways:
Save soap and waste paper.

Last night I shot a burglar in my pyjamas.

I live by the river; drop in sometime.
  • News headlines often suffer from this problem:
Panda mating fails. Veterinarian takes over.

Weak police force due to lack of intelligence.

Blair unveils economic plan. More lies ahead.

The Faulty Dilemma

This is when the either/or reasoning is used in a faulty way. The Law of Non-Contradiction applies when there are two mutually exclusive options being presented. With a faulty dilemma, 2 options are given by the speaker while in reality there are more options.

You’re either a communist or a fascist.

Either God exists or evil exists.

The dilemma in this second statement is faulty – the person assumes that there is such a thing as evil and therefore is assuming that there is such a thing as good. If there is such a thing as good, how, with that reasoning, can they disprove God?

Either dead people come back to life and are married to the people they were married to before or there is no resurrection.

The Slippery Slope

This reasoning aims to show that a particular proposition is unacceptable because of increasingly unacceptable events which are shown to follow from the proposition. It can be used positively – to help one see where a particular line of thought may end up, but as a means of logic it is fallacious.

If women are educated then they will not want to stay at home and be good wives and mothers and there will be unrest in our society.

If you pass legislation against abortion on demand then poor women will not be able to afford to keep their babies and we’ll have dangerous back-street abortions.

If I make an exception for you then I have to make an exception for everyone.

Here is this man performing many miraculous signs. If we let him go on like this, everyone will believe in him and then the Romans will come and take away both our place and our nation. (John 11:47-8)

The Complex Question

This is when two otherwise unrelated points are conjoined and treated as a single proposition. The person who is replying is expected to accept or reject both together when in reality one may be acceptable, while the other is not:

Does your mother know you are stupid?

Is it right to pay taxes to Caesar or not?

In this second question the complexity is assumed: the implication is that as the Romans are evil conquerors, if you pay you are on the side of evil. But, if you propagate not paying you are breaking the law. Either you are on the side of evil or you defy Rome. This was a trap for Jesus – a complex question is often powerful because of the assumptions of the cultural context from which it comes. Be careful before jumping in with a yes or no answer – identify what is going on, as Jesus did.

Have you stopped beating your wife?

Psychological or Emotional

  • Appeal to force – the listener is told that certain negative consequences will follow if they do not agree with the proposition:
Anyone who does not agree with the new company policy will be fired.
  • Appeal to pity – the listener is encouraged to agree to a proposition because of the pitiful state of the speaker:
You mean you don’t think this article is good? I spent so much time on it.

God could not possibly send my lovely granny to hell.

How can you sentence this man to life in prison? Who will look after his wife and children?
  • Appeal to consequences – the speaker points to a negative consequence of a particular proposition to show that the proposition is false:

If we allow these people to preach the gospel, then our culture will be changed, therefore we should not allow them to preach.


  • Character Assassination – this is when a person or a group are attacked rather than the proposition itself.
Members of the jury, are you going to believe that alcoholic, or this up-standing member of society?

Remember here – the up-standing citizen could be the witness in a drink drive accident. Or we could take it the other way round – the driver of the car could be the perpetrator and the alcoholic the witness in which case the character assassination says the alcoholic’s testimony is invalid because he is an alcoholic.

Here is a glutton and a drunkard, a friend of tax collectors and sinners. (Mathew 11:19).
  • Appeal to Popularity – this is when something is argued to be true on the basis that a large number of people hold to it:
This is the 20th century. No one believes that rubbish anymore.

How can millions of people be wrong in their sincere beliefs?

But Mum and Dad, everyone is doing it.
  • Hasty Generalisation – this is the fallacious reasoning by which a person will write off an idea or practice, when his or her exposure to the whole is not sufficient to do so.
All Italians are bald – at least the one I saw was.

All churches are boring – well the one I went to 10 years ago was.

Begging the Question

In this kind of fallacy a person will make an assumption and go through a process of circular reasoning whereby their original assumption appears to be the conclusion. They haven’t proved anything – the argument is circular. We can see this in the reasoning of the philosopher David Hume. He makes an assumption:

1. The Laws of nature cannot be violated. Assumption
2. Miracles are violations of the Laws of Nature. Statement of the obvious
3. Therefore miracles do not occur. Conclusion in line with assumption

There is so much evil in the world, if there was a God he would not allow all this suffering, that is why I am an atheist.

Straw Man

This is where a person makes a case appear much weaker than it actually is:

Christians eat the flesh and blood of their leader, cannabalism is barbaric and wrong.

Christianity is a list of dos and don’ts and has gone out of date. (argument versus legalism)

Because atheists can’t sustain any moral framework you can’t trust what they say.

Genetic Fallacy

This is the reasoning by which ideas or a people are rejected on the basis of their origins:

Can anything good come out of Nazareth?

Christians in Africa are more primitive and believe the Bible literally.

You only say that because you are an evangelical.

Post Hoc Fallacy

This is where 2 events running in parallel are fallaciously seen as related causally:

The telephone rings and the doorbell immediately sounds therefore the telephone ringing must have caused the doorbell.

My car has been playing up and will not start. In frustration I kick the tyre. Suddenly the car starts – therefore the tyre-kicking caused the car to start.

© 2006 Michael Ramsden