How to Win Every Argument: The Use and Abuse of Logic (2006)

Petitio princlpll 123

Life's judgements often call for trade-offs. Those who have
made their balance and come down in favour are apt to try to
persuade others by emphasizing only the positive side. The
unwary should remember that their own scale of values might call
for a different judgement, once they consider all of the factors.

All of the arguments support the new road. It means progress; it means

prosperity; it means a future for our town!

(And it really is rather unfortunate that they have to pull your house

down to build it.)

There is a clever version of one-sided assessment which you

should use when persuading others to agree with your judge-

ment. This involves making a purely token concession to the case

against you, by referring to one of the weaker arguments on the

other side before you launch into the overwhelming arguments

in favour. This polishes your case by adding to it the gloss of

apparent objectivity.

Of course, if we bought a bigger car, we'd need to make new seat covers.

But think of the convenience! All the shopping would go in the back; we

could use it for holidays; you could pick up the children in comfort; and

its extra speed would cut down our journey times.

(Sold, to the gentleman with the fallacy.)

Petitio principii

The fallacy of petitio principii, otherwise known as 'begging the
question', occurs whenever use is made in the argument of
something which the conclusion seeks to establish. The petitio is
a master of disguise and is capable of assuming many strange