Final answer:
Mr. Peters does not use his third wish in the story 'The Third Wish', symbolizing acceptance and the importance of decision-making.
Step-by-step explanation:
In the short story The Third Wish by Joan Aiken, Mr. Peters does not make a third wish before the story ends. Instead, after using his first two wishes, he chooses not to use his third wish and leaves it unused on a piece of paper. The first wish was to rescue a swan, and the second wish was to turn the swan into a woman so she could be his wife. When he realizes that she is unhappy in human form, he uses his second wish to turn her back into a swan. The idea of the third wish remains open to interpretation, symbolizing perhaps the acceptance of life as it is and the importance of thinking carefully before making decisions.