Are commas and dashes truly interchangeable?

Question

My English teacher told me that "dashes and commas are interchangeable". For instance, "My friend, Alex, ran to the store." and, "My friend–Alex–ran to the store." are both grammatically correct sentences and have the same meaning. However, is, "My friend–Alex, ran to the store." a correct sentence? Or can the sentence only have one or the other when a dependent clause is inserted into an independent clause like that?

Answer 1

Commas and dashes are both punctuation marks used to separate and emphasize elements within a sentence, but they are not entirely interchangeable. Commas are more commonly used to separate independent clauses in a compound sentence or to separate items in a list. They can also be used to set off non-essential information within a sentence, providing additional details without changing the main meaning. Dashes, on the other hand, are used to emphasize information within a sentence, usually by setting it off from the rest of the text. They can indicate a pause, create a strong break, or draw attention to a specific phrase or clause. While dashes can sometimes be used in place of commas for emphasis, they are generally bolder and more emphatic in their effect.

In terms of usage, commas are typically seen as more formal and standard in everyday writing, while dashes are often used more sparingly for added emphasis or to convey a more informal tone. Both punctuation marks serve different purposes in sentence structure, with commas helping to clarify sentences and maintain a smooth flow of information, while dashes are used for emphasis and to create a dramatic effect. It's also worth mentioning that different writing styles or style guides may warrant different approaches to these punctuation marks.

Answer 2

Ahhh, no, Friend. Your teacher probably did not mean to imply that these two are exchangeable in all circumstances.

In the case of the situation you brought up, i.e.: my friend - Alex - ran to the store, yes. They are interchangeable. This is because the information surrounded by these punctuation marks is an appositive, or additional information that does not change the grammatical completeness of the sentence. Whether you mention your friend's name or not in that sentence, the friend still ran to the store (the subject-verb-object structure of the sentence is still in tact).

For appositives, you must use one or the other (you can use either a set of commas or a set of dashes and it comes out the same), but you can't use both at the same time.

Further question - are you familiar with all the reasons for comma usage? Would love to touch base with you on this.