A parenthesis is one or both curved marks, ( ), used to contain a parenthetical expression. Parentheses is the plural of parenthesis although for the sake of promoting proper usage lets assume it’s also an even number. Checking a variety of handy on-line references you will find that parentheses are used to clarify a statement (such as you are probably better off learning the rules of punctuation usage from a book and not some random blog post). Parentheses are also great for making asides (like I’m glad that last parenthetical statement didn’t stop you from reading). It is also possible to use parentheses for either the singular or the plural of an item, such as cow stomach(s). In summary, parentheses are useful for (1) including a clarification, (2) making an aside(s) and (3) enclosing the numbers in a list of items.
It has been noted that overuse of parentheses is perhaps a sign of poorly written text. But there don’t seem to be any exact rules for over-use. Certainly the use of an odd number of parentheses is discouraged but given rampant ASCI emoticons ; ) it’s probably hard to enforce on a strictly algorithmic basis. At this point in the post, if it weren’t for the recent NYRB article reviewing all of blogging, that I would make up some fake reference like I found this blog post by Sucha Phake who has just written a recently published book Parentheses and How They Saved Humankind (and Zeroed My Inbox) but I’ve been shamed into thinking fictional non-fiction is not a valid genre (maybe). But I did do a search for a “parentheses expert” using the OMV (“Oracle of Mountain View“) to find that there is “no such thing” as a parentheses expert. Going out on a limb, I’d say if you have more than two parentheses per paragraph it might be time to go for a re-write (that is unless you’re writing about parentheses of course).
As far as blogging goes, parentheses are used for a wider variety of purposes with greater nuance. For example there are (1) the inclusionary aside “(Mills is a fan of Clay’s catchphrase)“, (2) the elusive English gender neutral pronoun “s(he)“, (3) the historically qualitatively quantitative “(In those days, getting a few hundred messages for a Web site launch was a sign of runaway success.)” and (4) quasi-euphemistic retrograde anti-stereotyping “(old customers)“. It is left as an exercise to the reader to find more examples of blogging and ( )’s.