The tu quoque fallacy is committed when it is assumed that because someone else has done a thing there is nothing wrong with doing it. This fallacy is classically committed by children who, when told off, respond with “So and so did it too”, with the implied conclusion that there is nothing wrong with doing whatever it is that they have done. This is a fallacy because it could be that both children are in the wrong, and because, as we were all taught, two wrongs don’t make a right.
(1) The Romans kept slaves.
(2) We can keep slaves too.
This argument commits the tu quoque fallacy because it assumes that if someone else does a thing then it’s okay for us to do it too. It does not follow, however, from the simple fact that the Romans kept slaves, that there is nothing wrong with keeping slaves. It is plausible to think that the Romans acted immorally in keeping slaves, and that we would act immorally if we followed their example. The conclusion of the argument therefore does not follow from its premise.
Examples of the tu quoque fallacy occur all the time. For instance, in an article entitled Man United defend ticket price rise, BBC Sport reported:
“Manchester United have hit their fans with a 12.3% average rise in season ticket prices for the next campaign. A top-price ticket will cost £38 and the cheapest £23… But United have defended the price rises, saying they compare favourably with the rest of the Premiership. ‘We do not know what most of our rivals will charge next year, buy even a price freeze across the rest of the Premiership would mean that next year only seven clubs will have a cheaper ticket than £23 and nine clubs will have a top price over £39 – in some cases almost double,’ said Humby [Manchester United finance director].”
The representative of Manchester United’s argument was essentially this: “Other Premiership clubs charge more, therefore our ticket prices are justified.” This commits the tu quoque fallacy because it’s quite possible that all clubs, including Manchester United, overcharge for their tickets.