Matthew 22:
23The same day Sadducees came to him, who say that there is no resurrection, and they asked him a question,
Let proposition R1 = there is resurrection.
The Sadducees do not believe in the resurrection. They believe ¬R1.
24saying, “Teacher, Moses said, ‘If a man dies having no children, his brother must marry the widow and raise up offspring for his brother.’ 25Now there were seven brothers among us. The first married and died, and having no offspring left his wife to his brother. 26So too the second and third, down to the seventh. 27After them all, the woman died. 28In the resurrection, therefore, of the seven, whose wife will she be? For they all had her.”
Yet, their question assumes the resurrection.
Are the Sadducees being sarcastic?
Not exactly. In modern logic terminology, they are attempting a proof by contradiction by assuming the negation or opposite of what they are trying to prove.
Assume R1.
Whose wife will she be for they all had her?
Accordingly to their logic, there is no answer to this question. Therefore the assumption R1 is false.
End of Proof so they thought. However, technically speaking, they did not supply a formal contradiction in their proof. They only supply a question that they cannot answer.
Now, it is Jesus' turn. Jesus also uses proof by contradiction (aka indirect proof):
31 as for the resurrection of the dead, have you not read what was said to you by God: 32‘I am the God of Abraham, and the God of Isaac, and the God of Jacob’? He is not God of the dead, but of the living.”
Jesus believes R1.
Using proof by contradiction. Jesus assumed ¬R1.
But then in Exodus 3:
6 And he said, “I am the God of your father, the God of Abraham, the God of Isaac, and the God of Jacob.”
The LORD is the God of Abraham.
Abraham is dead.
The LORD is the God of the dead = D1.
But in reality, Matthew 22:
32 I am the God of Abraham, the God of Isaac, and the God of Jacob’? He is not the God of the dead but of the living.”
Let proposition L1 = The LORD is the God of the living.
D1 = ¬L1.
Jesus has found a formal contradiction!
Therefore, the opposite of the assumption is true: There is a resurrection of the dead.
End of Proof.
Both the Sadducees and Jesus use the method of proof by contradiction. Because of their difference in beliefs, their initial assumptions are opposite to each other. The Sadducees failed to supply a formal contradiction to complete their proof. Jesus, on the other hand, did.