Final answer:
A dash is used to emphasize the separation of ideas or lists, as well as to explain, summarize, or illustrate a thought.
Step-by-step explanation:
A dash is used to emphasize the separation of ideas or lists and to explain, summarize, or illustrate a thought. For example, in a sentence like "The roof of that car was covered in Astroturf—a strange sight!", the dash is used to emphasize the phrase "a strange sight" and separate it from the rest of the sentence. A dash is used to emphasize the separation of ideas or lists, or to explain, summarize, or illustrate a thought. Unlike a comma, which alerts readers to a brief pause within a sentence and often sets off essential and nonessential information, the dash serves to create a stronger separation. When choosing to use a dash, you are ensuring that the phrase or list you are setting off is given more importance and stands out more to the reader. For example, in the sentence 'The U.S.S. Constitution became known as "Old Ironsides" during the War of 1812—during which the cannonballs fired from the British H.M.S. Guerriere merely bounced off the sides of the Constitution,' the part after the dash is heavily emphasized and is crucial for understanding the significance of the nickname 'Old Ironsides.' The use of dashes also indicates a contrast or a change in direction in a sentence. This is particularly useful when the writer wishes to draw the reader's attention to a significant shift or to introduce additional, often dramatic, information. Therefore, in contexts where a writer wants to underscore a certain point strongly, the dash becomes the punctuation of choice.