Soundness

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An argument is \emph{sound} just if it is logically valid and its premises are true

Whether a sentence is true may change as the world changes.

The same applies to whether an argument is sound.

Whether an argument is logically valid not does change as the world changes.

	1.	All cats are grey
	2.	Catmando is grey
	3.	Catmando is a cat

‘Catmando, Joint leader of the Official Monster Raving Loony Party from 1999 to 2002.’ This argument isn’t valid so of course it won’t be sound. Let’s fix that

	1.	All cats are grey
	2.	Catmando is a cat
	3.	Catmando is grey

‘Catmando, Joint leader of the Official Monster Raving Loony Party from 1999 to 2002.’ Now the argument is valid, but is it sound?