Petitlo prindpii 125
All arguments which purport to prove the unprovable should
be carefully scrutinized for hidden petitios. Arguments in support
of ideologies, religions or moral values all have it in common that
they attempt to convince sceptics. They also have it in common
that petitios proliferate in the proofs.
Everything can be defined in terms of its purpose.
(Never be surprised when a discussion starting like this ends up
'proving' the existence of a purposive being. If things are admitted at
the outset to have a purpose, then a being whose purpose that is has
already been admitted. This is a petitio prindpii disguised as a proof.)When using the petitio yourself, you should take great care to
conceal the assumption of the conclusion by skilful choice of
words. Particularly useful are the words which already have a
hidden assumption built into them. Words such as 'purpose' fall
into this group. Philosophers always go into battle with a huge
stockpile of these words, especially when they try to tell us how
to behave. The obligations they wish to impose upon us are
hidden away in words like 'promise'. It looks like a straight,
factual thing, but it has an 'ought' tucked away in its meaning.
The important thing to remember about the petitio is that it is
supposed to look like an argument in support of a case. You
should therefore spatter it with argument link words such as
'because' and 'therefore', even if it is no more than a simple
rewording.
When pushed into a corner you can often effect a dramatic
escape with a well-chosen petitio by combining both the
assumption of a general truth, and a rewording of the
conclusion.
We should not sell arms to Malaysia because it would be wrong for us to
equip other nations with the means of taking human life.