Rules Do Change
Spacing after Periods, Colons, Question Marks, and Exclamation Marks
Originally, typewriters had monospaced fonts, so two spaces after ending punctuation marks such as the period were used to make the text more legible. However, most computer fonts present no difficulty with proportion or legibility, so use just one space after a period, colon, question mark, or exclamation point at the end of a sentence. You will not be struck by lightning, I promise!
Quotation marks and Punctuation
In Grandma’s day, a period used with quotation marks followed logic: Example: Myrtle said the word “darn”. The period went outside the quote because only the last word was in quotation marks, not the entire sentence. Example: Myrtle said, “I would never say that.” The period went inside the quotation mark because the entire sentence is a quote.
Today, in American English usage, the period always goes inside the quotation mark.
Example: Myrtle said the word “darn.”
This does not follow logic, but it makes life easier for those of us who have enough to think about besides punctuation.
As time has gone on, we have shortened some words and dropped the former plural form.
Example: The words memo and memos used to be memorandum and memoranda.
With the word data, we no longer see the singular datum used at all. Data is now normally used in both the singular and plural form.
Example: The data are being tabulated. The data is useful to the scientists.
Yet other words still retain their original spelling and plural form.
Example: curriculum (singular) and curricula (plural).
In “the old days,” you may have been scolded for starting a sentence with but, and, or because. But you wouldn’t have deserved that scolding. Just make sure that if you start sentences with these words, you follow them with independent clauses.
Good Examples:
But she would never say such a thing!
Because of this bee sting, my arm is swollen.
Bad Examples:
And washed the car.
Because she asked.
Posted on Friday, December 1st, 2006 at 8:54 pm

I have always done two spaces after a period. You’re making me rethink this a bit. And I’m guessing it’s all right to use not only “but” at the beginning of a sentence but also “or” and “and.” Did I do the previous sentence correctly?
Yes!
Will I be wrong in suggesting the following changes in the texts used above:
1. Grandma’s days…instead of Grandma’s day.
2. And I’m guessing if it’s all right…
It’s “Grandma’s day,” not “Grandma’s days” because this is an expression or idiom in the language.
I’m not sure what you are referring to in your second comment, Ravi.
Thanks Jane. I had always used ‘days’.
The second one refers to the second sentence used by Tom.
Which is correct….data was used or data were used?
“Data was” or “Data were” are both correct. In the old days, “datum” was the singular form of “data” but now “data” is used as both a singular and plural.
Some of these rules are merely interpretations and beliefs of rules. Remember that English is not math. Coordinating conjunctions (such as and, but, or, etc.), in my OPINION, should not be used at the beginning of sentences. Save that for the sports writers. As for the two spaces, keep up the traditional interpretation; two spaces much more clearly indicate a new sentence to the reader.
Sorry to correct you but ‘Datum’ IS still used.
As a science student, every single lecturer I have had so far is annoyed by the misuse of the word ‘Data’ as a singular form, as ‘datum’ is the singular form and is still in use.
Good for you for knowing the difference between “datum” and “data.”
While I disagree with much of the advice given above, (such as starting sentences with coordinating conjunctions is advisable in an academic paper), I have to agree that data can and should be considered singular. In English is possible to have singular nouns which sometimes represent a collective, as in the words class, research, etc. Also, it is normal for a loanword from a foreign language to eventually behave according to the rules of the language which has borrowed it. There is no reason for this word to behave according to the rules of Latin just because it came from Latin. If the sciences want to hold on to “datum” let them do so; outside of the sciences, data should be acceptable.
Thank you for your comment. It was not my intention to encourage beginning sentences with coordinating conjunctions in an academic paper. I was only acknowledging the acceptability of doing so in American English.