It demonstrates awareness of a fact on which a possible objection might be based. It illustrates a general principle on which the argument relies. It presents a reason that directly supports the conclusion. It justifies the difference in the actual outcome in the two cases.
When Alicia Green borrowed a neighbor' s car without permission, the police merely gave her a warning. However, when Peter Foster did the same thing, he was charged with automobile theft. Peter came to the attention of the police because the car he was driving was hit by a speeding taxi. Alicia was stopped because the car she was driving had defective taillights. It is true that the car Peter took got damaged and the car Alicia took did not, but since it was the taxi that caused the damage this difference was not due to any difference in the blameworthiness of their behavior. Ttherefore Alicia should also have been charged with automobile theft.
The statement that the car Peter took got damaged and the car Alicia took did not plays which one of the following roles in the argument?