I am very confused by these, and even when I understand other people's usage of them I find it difficult to know when to employ them myself. For this reason, I am trying to make my own examples and see if I get them correct. Please understand, English is not my first language, but I have never learned grammar in my native language either. I hope that what I'm saying is comprehensible to you.
In the following examples, I'll be using a period in place of the em dash or semicolon, because I am utterly confused as to which one should be used.
English is not my first language, and I'm having trouble with the grammar. Specifically semicolons and dashes.
Don't ask Jim to fix your car. That sort of thing would be better handled by Steve.
The question isn't what you can take away from this, but what you can learn in the process. / The question isn't what you can take away from this. It is what you can learn in the process.
Normally I would use a semicolon in all of these instances, but recently I have come to learn that this is incorrect usage.
Any help is greatly appreciated.
Best Answer
Dashes can be used in place of parentheses to indicate an aside or qualifying statement. I don't think either has a place in any of your examples.
Generally speaking, for the same reason you're having a hard time understanding their use, it's a good idea to avoid using semicolons altogether. The semicolon is intended to separate two sentences where the second sentence clarifies or extends the first. In practice, they're often used incorrectly and there is ample evidence that they confuse readers and translation software. A comma or period would often suffice.
It's good advice to use the simplest punctuation possible. That often means using the simplest sentence construction possible as well. Here is how I would punctuate your examples:
Note here that the wording is more specific so that the second clause merely clarifies. It could be thought of as a contraction of this more verbose version:
Or, if you really felt the need to use that spare semicolon:
Your second example is fine as is; it's completely clear in meaning as two sentences (see what I did there?).
Your third sentence provides a great example of the many ways to associate two sentences. The first is very clear, but awkward and wordy. The second is probably most confusing to readers because the second sentence is quasi-grammatical. "it" implies "The question" here. The third is a rather elegant construction to my native English comprehension. Does the conjunction "but" imply the same meaning to you, however?
These all mean exactly the same thing. From your perspective, take the construction that makes the most sense and use that consistently in your writing. Much great writing can be done without any semicolons at all.
Finally, note that your last example is a rhetorically loaded construction in English. I'm sure "Not this, but that" phrasings are encountered in many languages. Here's a famous example:
In these cases, simple, repeated, parallel constructions work in your favor in spite of the punctuation:
Be clear. Be consistent. Remember that many writers don't actually know the rules of punctuation. My apologies for rambling.