The whole conditional 'If electricity is supplied, the fan runs' is false when electricity is supplied and the fan does not run. Merely saying 'If electricity is supplied, the fan does not run' forms a different conditional claim, not automatically the logical negation of the entire first conditional. Deny the complete assertion, not simply one clause.
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Opposition in conditional statements
Contradiction and the Eight Conditions
The whole conditional 'If electricity is supplied, the fan runs' is false when electricity is supplied and the fan does not run. Merely saying 'If electricity is supplied, the fan does not run' forms a different conditional claim, not automatically the logical negation of the entire first conditional. Deny the complete assertion, not simply one clause.