Question
Determine the validity of the following arguments using the direct method of truth table:
$P \rightarrow (Q \rightarrow R)$
$\sim R$
$\therefore Q \rightarrow \sim P$

Answer

Combining the two bases of this argument as a whole, the argument will be as follows:
$[P \rightarrow (Q \rightarrow R)] \&\ \sim R$
$\therefore Q \rightarrow \sim P$
Truth Table:
  Support Statement The resulting statement
  $1$ $2$ $3$ $4$ $5$ $6$ $7$ $8$ $9$
$P$ $Q$ $R$ $\sim P$ $\sim R$ $Q \rightarrow R$ $P \rightarrow (Q \rightarrow R)$ $[P \rightarrow (Q \rightarrow R)]\ \&\ \sim R$ $Q \rightarrow \sim P$
$1$ $T$ $T$ $T$ $F$ $F$ $T$ $T$ $F$ $F$
$2$ $T$ $T$ $F$ $F$ $T$ $F$ $F$ $F$ $F$
$3$ $T$ $F$ $T$ $F$ $F$ $T$ $T$ $F$ $T$
$4$ $T$ $F$ $F$ $F$ $T$ $T$ $T$ $T^*$ $T^*$
$5$ $F$ $T$ $T$ $T$ $F$ $T$ $T$ $F$ $T$
$6$ $F$ $T$ $F$ $T$ $T$ $F$ $T$ $T^*$ $T^*$
$7$ $F$ $F$ $T$ $T$ $F$ $T$ $T$ $F$ $T$
$8$ $F$ $F$ $F$ $T$ $
$
$T$ $T$ $T^*$ $T^*$
  $1(\sim )$ $3(\sim )$ $2, 3(\rightarrow)$ $1, 6(\rightarrow)$ $7, 5(\&)$ $2, 4(\rightarrow)$
Judgment of the validity of the argument: A total of nine columns have been formed in the above fact sheet. In which the column no.$ 8th$ base statement and column no.$ 9$ is the introduction of the result statement. Row out of the total eight rows of the truth table. The base statement in $4, 6$ and $8$ is the truth $‘T’$ and all the resulting statements in the same row are also the truth $‘T’.$ Hence this argument is standard.

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