Em Dashes as seperation of a preposition phrase

Question

Can em dashes be used to separate prepositional phrases? So that phrase is only used as to modify the noun directly before it, and to the rest of the sentence is non-existent.

Examples:

• Truth is I — at my position in time — strive to succeed. [Em dashes are used to make clear that I strive, my position in time has nothing to do with me striving.]
• The pencil has yellow scrapes — which were made by Billy who has a multitude of diseases — which are concerning. [Em dashes are used to make clear that the scrapes are concerning. Not in any way is this sentence saying Billy's diseases concerning.]
• The alien looking man — with a red lizard that seems as if it might run—ran quickly. [Em dashes are used to make clear that the man ran, not the lizard (even those the lizard looks like it might run)]

Do the em dashes do what I say they do in the sentences? If yes, then the answer to this question would be yes. Otherwise the answer would be no.

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Thank you.

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Answer 1

The use of dashes doesn't necessarily make the phrase completely independent of the rest of the sentence.

Also, in terms of punctuation these should simply be called dashes. If you decide to make your dash the same width as the letter 'm' then it is an em-dash, but that's merely a typographical decision.

Truth is I—at my position in time—strive to succeed. [Em dashes are used to make clear that I strive, my position in time has nothing to do with me striving.]

I don't think this necessarily makes clear that your position in time has nothing to do with your striving.

The pencil has yellow scrapes—which was made by Billy who has a multitude of diseases—which are concerning. [Em dashes are used to make clear that the scrapes are concerning. Not in any way is this sentence saying Billy's diseases concerning.]

(You mean "which were made by Billy, who".) Certainly the most natural reading is that the text enclosed by the dashes is a parenthetical aside, and the yellow stripes are the thing that's concerning. I don't think that this is the only possible meaning, though. Sometimes a sentence has only one dash - so your second dash could be intepreted as starting a second parenthetical aside (one relating to the diseases) rather than as the end of the original aside.

The alien looking man—with a red lizard who seems as if it might run—ran quickly. [Em dashes are used to make clear that the man ran, not the tattoo (even those the lizard looks like it might run)]

It's a bit confusing to personify the lizard here. (I'd write "that seems" rather than "who seems".) The repetiton of the verb "run" has the potential to confuse the reader, who might also think the lizard is a real lizard rather than a tattoo, unless that was explained earlier in the text. But I agree that the sentence must be read as meaning that the man ran, not that his tattoo ran.

Answer 2

Yes, em dashes can be used to replace commas but are "less formal". (Correct em dash usage).

I would however argue that your example sentences don't convey exactly what you mean to convey.

In the first sentence, there is no reason to include "at my position in time" unless this isn't the case at other points in time.

In the second sentence it is unclear whether you're referring to the scrapes or the diseases so I would write it as, "The yellow scrapes on the pencil—which were made by Billy who has a multitude of diseases—are concerning." In this case were refers to the scrapes made by Billy and not the pencil therefore we must use the plural form 'were'.

In the third sentence the use of the em dashes is correct but the word who should be replaced with "which" or "that" i.e. "The alien looking man—with a red lizard tattoo (I assume you forgot to add in the word tattoo here) which seems as if it might run—ran quickly".

Answer 3

Different elements of punctuation serve different purpose. For example, parentheses are said to "whisper" while dashes are said to shout. Commas are somewhere in-between. Otherwise, all three use more or less the same grammar:

Billy, who was known to be prankster, put the frog down Mary's dress.

Billy -- who was known to be prankster -- put the frog down Mary's dress.

Billy (who was known to be prankster) put the frog down Mary's dress.

Otherwise your examples are not quite grammatically or stylistically correct, but they are close.

Truth is I -- in my position at this time -- strive to succeed.

The yellow scrapes on the pencil -- made by Billy who has a multitude of diseases -- are concerning.

The alien-looking man -- who had a red lizard that looked like it could scamper off at any moment -- ran quickly.

I changed the order of the sentences and a few words here and there for clarity. In general you should avoid using the same word twice in a sentence except for intentional emphasis, otherwise it can be confusing.

Side note: The "em dash" or "long dash" generally only appears in typewritten documents because it's not a key on a standard keyboard. Instead we substitute with two regular dashes "--". The dash should also not be confused with the hyphen, used to connect words like "alien-looking".