Monday, 26 August 2013

Critical Thinking 4: Validity

Higher Philosophy Podcast
Critical Thinking: Validity

This is available as an MP3 or to download as a podcast through iTunes
for Desktop and Apple devices, as well as PodcastHD for Android Devices.

Arguments cannot be true or false, they can only be valid or invalid.  The terms valid and invalid relate only to the structure of the argument.  Even though we use the term every day we must distinguish common use from philosophical use.  Validity is considers the connections between the premises and the conclusion.  A valid argument is one in which the premises follow a logical flow to the conclusion, forcing the audience to accept the conclusion.  If an argument is valid, you cannot have true premises and a false conclusion.  So if the premises are true you are guaranteed a true conclusion.  However, that is not to say you can’t have false premises and a true conclusion – you can – and the argument would still be valid.  Why?  Simply because the structure of the argument is valid – not the content, consider the following:

In Argument A and B you can see the conclusion leads naturally leads from the premises; both arguments are therefore valid.  P1 and P2 in Argument A are true, this guarantees us a true conclusion; however in Argument B we can challenge the truth of P1 – all humans like pizza.  Do they?  They might, but the argument doesn’t demonstrate this and moreover we know this isn’t the case.  Already you can see epistemological concepts creeping into CT – it is tempting but at this stage keep the two topics separate.

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