From the Lynch Guide to Grammar:
Ellipses. The ellipsis (plural
ellipses) is the mark that indicates the omission of quoted material, as in "Brevity is . . . wit" (stolen shamelessly from an episode of
The Simpsons). Note two things: first, most typing manuals and
house styles prefer the periods to be spaced, thus:
Brevity is . . . wit.
(In electronic communication it's sometimes convenient, even necessary, to run them together, since line-wrap can be unpredictable.) Second, and more important, is the
number of periods. The ellipsis itself is
three periods (always); it can appear next to other punctuation, including an end-of-sentence period (resulting in
four periods).
Use four only when the words on either side of the ellipsis make full sentences. You should
never use fewer than three or more than four periods, with only a single exception: when entire lines of poetry are omitted in a block quotation, it's a common practice to replace them with a full line of spaced periods.
One other thing. Although it's a matter of
house style, note that it's usually unnecessary to have ellipses at the
beginning or
end of a quotation; they're essential only when something's omitted in the
middle. There's no need for ". . . this . . ." when "this" will do: readers will understand you're not quoting everything the source ever said, and that there will be material before and after the quotation you give.
The only time it's advisable is when the bit you're quoting isn't grammatical when it's standing on its own: "When I was a boy . . ." — that sort of thing.
[Entry revised 12 July 2005.] Wholeman
Usage of "..." at the end of a sentence 
Linear Mode
