Logic

The art of argument

The early Greek philosophers not only came up with many of the founding ideas of western thought, they bequeathed an intellectual toolkit, a set of procedures for thinking clearly. Philosophy literally means ‘the love of wisdom': the rules of logic help the thinker find his or her way through the complexities.

More on the word ‘logic': The Greek word logos means ‘word', ‘idea', ‘principle' or ‘reason'. It is the root of the modern ‘-ology' as well as of ‘logic' itself.

The pitfalls of reasoning

Reasoning is full of traps for the unwary:

• A statement might easily be true and yet still misleading
  • E.g., To say that ‘every fifth child born in the world is Chinese' may well be statistically accurate, but it does not mean that the youngest of any five British, American or Guatemalan brothers and sisters will be Chinese.
• Another very common fallacy was recognized by the Romans, who described it in Latin: ‘post hoc ergo propter hoc' – ‘after this, therefore because of this'
  • E.g., If I crash my car after a visit to Birmingham, it is not necessarily true that I crashed because I had been in Birmingham. (On the other hand, there might well have been a ‘causal connection' with the wine I drank there with lunch.)
• One false step that can easily be taken in argument has been nicknamed the ‘No true Scotsman' move in modern times, though it was familiar enough to the ancients too
  • E.g., It might be claimed that ‘No Scotsman would ever have sugar on his porridge'. Yet an objector might be able to say ‘But Angus MacSporran is a Scotsman and he has sugar on his porridge'. The person making the original claim might then modify his or her position, saying, ‘Well, no true Scotsman would ever have sugar on his porridge.'
    • I.e., He or she would effectively be redefining the word ‘Scotsman' to mean something other than what it had always previously meant.

These examples are all obvious, but not all pitfalls are so immediately evident: often, wrongheaded statements may have an apparent ring of truth. Hence the development of logic and its rules.

Simple syllogisms

It was Aristotle who first formulated the idea of the syllogism, the idea that if certain things were accepted, other things might follow, according to set rules:

• E.g., It might be argued: All cows eat grass. Daisy is a cow. Therefore Daisy eats grass.
• This syllogism follows the typical form: major premise (general rule); minor premise (particular case); conclusion.

It is quite possible to make a mistake when arguing this way.

• E.g., All cows eat grass. Dobbin eats grass. Therefore Dobbin is a cow. (However, Dobbin is actually a horse.)
• Here, despite the fact that both major and minor premises were correct, an entirely mistaken conclusion has been reached.

Aristotle's rules clearly cannot prevent people from going wrong in their reasoning, but his analytical approach allows their mis-steps to be readily identified.

Logic and paradox

In the classic BBC TV comedy show Only Fools and Horses, the street-sweeper, Trigger, boasted proudly about the broom he had had, through thick and thin, for 20 years. For this ‘feat' he was awarded a medal from the local council. However, down the years, the broom has had no fewer than seventeen fresh heads and fourteen handles: how, he is asked, can he claim to have been using the same broom?

The paradox of ‘Trigger's Broom' is seriously discussed by philosophers today, since it poses important questions about exactly what it is that makes things what they ‘are'. This paradox was well known to the classical Greeks, though they saw it in terms of Theseus' ship – so extensively repaired and rebuilt that it might just as well be a different vessel. (Modern medical science has posed the question in an even more challenging form, asking how far we human beings remain ‘ourselves' when all the tissue that makes us up is constantly changing and being replenished over time.)

Related topics

Impact of classical literature: Aristotle, Plato

Other cultural references

Only Fools and Horses
 

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