To deny 'Every student has read the book,' it suffices to establish 'At least one student has not read the book.' 'No student has read the book' is a stronger claim and not the contradictory. Similarly, the negation of 'At least one student is present' is 'No student is present.' This is added practice extending the source's definition of contradiction.
Opening interactive controls...
Negating quantified propositions
Contradiction and the Eight Conditions
To deny 'Every student has read the book,' it suffices to establish 'At least one student has not read the book.' 'No student has read the book' is a stronger claim and not the contradictory. Similarly, the negation of 'At least one student is present' is 'No student is present.' This is added practice extending the source's definition of contradiction.