ISRO Scientist/Engineer 2017 Dec, Question 6, set A

❔ The proposition (P->Q)^(Q->P) is a

a) tautology
b) contradiction
c) contingency
d) absurdity

Answer is Contingency

as (P->Q)^(Q->P) equivalent to P⇔Q
These type of proposition are neither a tautology nor a contradiction.

Below truth table shows that the proposition holds true for two cases : so its contingency
here, 1 means true and 0 means false

P	Q	P⇔Q
0	0	1
0	1	0
1	0	0
1	1	1