How come?
And I would respectfully disagree. I don’t have my style books with me, but I do believe that’s too restrictive a guideline for colon usage. A colon is not an equals sign: an equals sign is an equals sign.
It doesn’t exactly disagree. The example of the colon use actually specifies the exact problem. That’s exactly the kind of use for which I suggested using the colon also. But if there’s a strong implied relationship that does not provide a direct instance of what was expressed in the preceding clause, the semi-colon is the appropriate choice.
Could you kindly provide me a sentence that demonstrates a correct use of the equals sign?
I agree that the colon doesn’t work particularly well in this sentence; the problem is that the reader isn’t expecting the sentence’s verb way back there after the list, because the colon usually means only clarification of a particular object. That’s why a dash – which signals that the thought will continue – is better in this case (as **pulykamell **pointed out).
If you really, really, want a colon in there, a better version might be: “Major trading hubs during the colonial era included the northeast capitals: Albany, N.Y.; Trenton, N.J.; Boston, Mass.; Providence, R.I. and Hartford, Conn.” This does, however, change the emphasis of the sentence, and also makes it a little more passive, so I like the dashes better, myself.
And since I’ve been sounding off on that, I’ll keep going.
My preference on state abbreviations is AP-style long ones (e.g. Mass.) rather than Post Office two-letter ones (MA), just because I think it looks nicer and reads a little easier. It just feels more like a sentence to me, and less like a database dump or computer code. It’s a personal style choice, though (unless you’re writing for the AP or someone else with a style manual).
And the equal sign ("=") is generally eschewed in formal writing, with the word “equals” being preferred. E.G. “Tom tried to prove that one plus one equals three, but failed.” However, if writing out an equation makes things clearer, then go for it, but remember that formatting might not always be preserved, so you could end up with “Einstein’s most famous equation is E=mc2.” Which might lead readers to think about forty percent of the Motor City Five instead of Einstein.
</smarmy pedantic mode off>
<wondering whether going back and changing all the “I” to the editorial “we” would increase my pedantic-points score enough to be worthwhile>
My wife has a semicolon; that’s what remained after the surgery.
And I would say your final sentence is better puctuated as:
A colon is not an equals sign; an equals sign is an equals sign.
I don’t understand why you would choose to use a colon there. Your sentence seems to fulfil the classic rule on semi-colon usage, which is to link two independent clauses that require a separation stronger than a comma, but less than a period.
CaveMike—as to why I prefer the old abbreviations, it’s because it looks much better to me in writing. The abbreviation in “Chicago, IL” sticks out like a sore thumb to me compared to “Chicago, Ill.” However, it’s just a matter of style. You may feel free to use two-letter postal abbreviations if your style allows it. Just be consistent. Also, if you do use the two letter abbreviations, the comma is not necessary, at least the United States Post Office doesn’t use it.
So, for our sample sentence we can have:
The northeast capitals—Albany NY, Trenton NJ, Boston MA, Providence RI, and Harford CT—were all major trading hubs during the colonial era.
I actually don’t mind the way this looks. Gets rids of a lot of punctuation clutter. However, I don’t know of any major stylebook that advocates this style.
Original Example: The northeast capitals: Albany, NY; Trenton, NJ; Boston, MA; Providence, RI and Hartford, CT were all major trading hubs during the colonial era.
I’m totally confused.
I was taught colons (not semicolons or dashes) introduce words, phrases, sentences, quotations or lists.
In the example above, those state capitals are part of a list. Why do you recommend a semicolon or dash (as opposed to a colon) be used? Though those 5 cities fall into your which is/are rule, I’ve always operated under the premise that semicolons are used like super-commas: which as Cliffy pointed out: “are used to connect what could otherwise be two whole sentences”. Are you certain your which is/are test pertains to semicolons or was there an misplaced semi in front of the colon?
One more Q: Shouldn’t semicolon be non-hyphenated word?
John, semicolons have two uses. The most important is to create a compound sentence without the need for a conjunction such as and, but, or, yet, etc. The second is as supercomma to set off a series that would typically be set off by commas but can’t be because it (typically) contains internal commas of its own. I don’t know the evolution of the mark, but to my mind the second use seems most likely to have been a borrowing of the mark from its standard (conjunctive) usage just because the typesetter needed something to replace the comma and the semicolon looked more like a comma than anything else around. puly and Xema, et al., are arguing about the first usage only.
I’m still confident of my position, Xema. The example from your link supports me. “John has a serious problem: he does not know how to relax.” uses the colon as an equals sign. The first part of the sentece leads the reader to ask “What problem?” The stuff after the colon answers it. That’s an equals sign. Alternatively, it’s an idea which could also be expressed with the words “it/which is.” That doesn’t fit the sentence “Singing lessons are nothing for me: I can’t sing.” For a colon to be acceptable here, it should answer the question “What me?” The stuff on one side of the colon should be equal to the stuff on the other side. John’s problem = he can’t relax. There’s no equal relationship in anything about the singing sentence. The second part amplifies and explains the first part, which is why it’s appropriate for a semicolon to be there in a way it’s not appropriate to use a semicolon for a non sequittr. But it doesn’t justify a colon.
–Cliffy
Yeah, “semicolon” is the preferred spelling. I believe “semi-colon” is allowable as well, but I prefer the hyphenless spelling (even though I had used the hyphen in my spellings. Brain fart.)
Yes, the colon is used to introduce lists, but not lists that are part of a complete sentence, as in your example. When introducing lists, a colon should follow an independent clause.
Thus, you would never punctuate this way:
Today for breakfast, I ate: oranges, milk, cereal, and toast. (Incorrect.)
but rather:
Today for breakfast, I ate oranges, milk, cereal, and toast. (Correct.)
I ate the following for breakfast: oranges, milk, cereal, and toast. (Correct.)
I confess, the “which/are” test is not as neat as I would like it. It just never would occur to me to use a colon in the manner you did. The reader doesn’t expect a sentence to continue on the other side of the colon. When I come to the verb “were” in that sentence, I’m surprised, because I’m not expecting to find a verb there, and I’m certainly not expecting to connect the verb to a word before the colon, because the punctuation doesn’t work that way.
Well, I was about to start a thread asking how to use it. Now, however, I will simply bump this thread, so that I can show that at least I tried to understand the concept. 
The semicolon has two principal uses, which are very well illustrated by Cliffy’s and John Buckwld’s posts.
The use of the colon in joining two independent clauses is very rare but important when it does occur. The second clause must be the logical explanation of the first, as though, standing by itself, it were “a list of one thing.”
“This led him to propound his famous law: The force of an action causes an equal reaction.”
The compound-by-semicolon sentence should include brief, related clauses. “He raged; she went stony-faced; the children cried.”