I've always had trouble with commas and semicolons. My understanding is that upon division of a sentence there is an essential part called a clause, and additional parts are then separated with commas, unless they are capable of being an essential part of a sentence, in which case a semicolon is used. The additional parts that are incapable of acting as an essential part are divided based on whether they are part of the same thought, because when spoken aloud these locations should bear a natural pause.

Is my understanding of how to use the comma and semicolon correct? If not, what is the correct way? Here are some examples of the way I think it should be done:


Bob headed down to the market for groceries; the market was out of everything.

The off-ramp led on; the off-ramp designer was fired.


Bob headed down to the market for groceries, but the market was out of everything.

Bob wanted to buy groceries, the market was out of everything, and so he decided to buy hardware supplies instead.

Please don't send me anymore potatoes Mary, Tom.


The tiny bees had knees, the knees were the-bees-knees, and everyone knew it except the bees; the big bees also had knees though theirs' were not the-bees-knees.

Bob wanted to buy groceries, but the market was out of everything; Bob bought hardware supplies instead of groceries.

  • I'm not sure if this question is in a good format for this site; it seems like you're asking too many things in a single question. – J.R. Aug 20 '14 at 1:19

Your understanding of the difference is essentially correct.

However, I was always taught (right through college, in fact) that semicolons are a wholly optional punctuation. It's such a good rule that native teachers often encourage students to ignore this kind of semicolon completely in favor of periods. They're slightly weaker than a period and meant to show association of thought, but they are essentially not grammatically necessary. If it joins related statements, it's not wrong to replace a semicolon with a period and to just start a new sentence. This is true because a proper semicolon is joining two independent clauses, and an independent clause is what forms a complete sentence. The amount of meaning you're losing by dropping the semicolon is very slight. So, if you're in doubt that a semicolon is even valid, put in a period and make sure each half is a whole sentence by itself.

I'd also agree with Jasper about finding this awkward without an "and":

Please don't send me anymore potatoes Mary, Tom.

It's a list or series, so the last two elements should be separated with an "and" or "or". I think most native speakers would also avoid it because it might sound like the phrase "Please don't send me anymore" was being directed at three things: "potatoes", "Mary", and "Tom." It wouldn't be confusing, but it would sound a bit weird. I'd expect to see:

Mary and Tom, please don't send me anymore potatoes.

And this clause is also confusing:

The off-ramp led on

"Led on" is somewhat ambiguous. "On what?" is the natural question for me, not, "On where?" This is partially true because "being led on" is an idiom for a person being deceptive or using false pretenses with another person. It's obviously not the right meaning based on context, but it makes using "led on" a bit less clear. I would expect to see:

The off-ramp led on to the freeway

Or even:

The off-ramp led back on to the same freeway.

That makes the error clear. "On" has a lot of uses, so it doesn't always convey context well.

Generally, the only other time semicolons are used is when you need to create a list or series of items and those items contain commas. In this case, the semicolon is acting like a slightly stronger comma. This is pretty rare, and it's usually a pretty easy to understand usage.


This kind of sentence has this general structure: the starting clause, which ends with a colon; the list of clauses, which are separated by semicolons; and the clauses themselves, which include commas.


All but one of your examples is correct, to my (American) eye and ear.

My quibble is with:

Please don't send me anymore potatoes Mary, Tom.

I think it would be better as:

Please don't send me any more potatoes, Mary and Tom.

(Also, I don't know what it means for an off-ramp to lead on. I assume that if I did, I would understand why the off-ramp designer was fired.)

I therefore think that your understanding of the difference between commas and semi-colons is correct. I was taught about this difference using different terms, so I am guessing at what you mean by "division of a sentence" and "additional parts". Your terms help you understand the difference, so they are good terms for you to use.

By the way, there are some other ways that commas can be used. The most common example is to separate items of a list that contains at least three items. For example:

  • Mary and Tom sent me potatoes. ("Mary and Tom" has only two items, so it does not have any commas.)
  • Jane, Mary, and Tom sent me tomatoes.
  • Jack, Jane, Mary, and Tom inundated me with fruits and vegetables.

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