Step by step
The question
Question: make the truth table of ¬(p → q).
1 Rows for p and q
Each letter can be true or false.
Two letters give 2 × 2 = 4 rows: every way they can go.
We make a table: a column for each letter, then a column for each part, from the inside out.
We write T for true and F for false.
p: the first half T, the second half F.
This way no row is missed.
q: T, F, T, F, down the column.
2 Column for p → q
We read the arrow as if, then.
p → q is a promise: if p, then q.
It is broken only when p is true and q is false.
So it is F only in row 2.
3 Column for ¬(p → q)
We read this sign as not.
¬(p → q) is the opposite of p → q: T becomes F, F becomes T.
So it is T only in row 2.
Careful!
If the if-part is false, the promise is not broken.
So F → F is T, and so is F → T.
The last column is the answer: when ¬(p → q) is true.
Top to bottom: F, T, F, F.
4 Check
Let's check row 1 by hand.
In row 1, p is true and q is true.
Put them in: ¬(T → T).
The inside first.
It gives F, as in the table.
Right!
Let's look back.
First: rows for p and q.
Then: column for p → q.
Then: column for ¬(p → q).
Last: check.