Editing Propositional calculus (section)

=== Validity and soundness ===
{{Main article|Validity (logic)|Soundness}}
An argument is '''valid''' if, and only if, it is ''necessary'' that, if all its premises are true, its conclusion is true.<ref name=":35" /><ref name="ms15"/><ref name=":36"/> Alternatively, an argument is valid if, and only if, it is ''impossible'' for all the premises to be true while the conclusion is false.<ref name=":36" /><ref name=":35" />

Validity is contrasted with ''soundness''.<ref name=":36" /> An argument is '''sound''' if, and only if, it is valid and all its premises are true.<ref name=":35" /><ref name=":36" /> Otherwise, it is ''unsound''.<ref name=":36" />

Logic, in general, aims to precisely specify valid arguments.<ref name=":21" /> This is done by defining a valid argument as one in which its conclusion is a [[logical consequence]] of its premises,<ref name=":21" /> which, when this is understood as ''semantic consequence'', means that there is no ''case'' in which the premises are true but the conclusion is not true<ref name=":21" /> – see {{section link||Semantics}} below.