Defining the structure of Parenthesis, the next aspects must be taken into consideration:
- a) Syntactical aspect;
- b) Morphological.
Speaking about Syntactical aspect, it is important to remember that parenthesis is also called simply brackets or round brackets, curved brackets, oval brackets. It contains material that could be omitted without destroying or altering the meaning of a sentence. In most writing, overuse of parenthesis is usually a sign of a badly structured text. They can be inserted into a passage with which it doesn’t necessarily have any grammatical connection. Parentheses are usually marked off by round or square brackets, dashes, or commas .
A dog (not a cat) is an animal that barks . The phrase not a cat is a parenthesis.
My umbrella – which is somewhat broken – can still shield the two of us from the rain . The phrase which is somewhat broken is a parenthesis.
Please, Gerald, come here! Gerald is both a noun of direct address and a parenthesis .
Parenthesis may be used in formal writing to add supplementary information, such as:
“Sen. John McCain (R., Arizona) spoke at length”.
They can also indicate shorthand for “either singular or plural” for nouns – e.g., “the claim(s)” .
Any punctuation inside parentheses or other brackets is independent of the rest of the text:
“Mrs. Pennyfarthing (What? Yes, that was her name!) was my landlady.” In this usage the explanatory text in the parentheses is a parenthesis.
Parenthesized text is usually short and within a single sentence. Where several sentences of supplemental material are used in parentheses the final full stop would be within the parentheses. Again, the parenthesis implies that the meaning and flow of the text is supplemental to the rest of the text and the whole would be unchanged were the parenthesized sentences removed .
There are a few general rules of using punctuation around parenthesis.
Rule1. Use parentheses to enclose words or figures that clarify or are used as an aside.
I expect five hundred dollars ($500).
He finally answered (after taking five minutes to think) that he did not understand the question.
Commas could have been used in the above example. Parentheses show less emphasis or importance. Em dashes, which could also have been used instead of parentheses, show emphasis.
Rule2. Use full parentheses to enclose numbers or letters used for listed items.
We need an emergency room physician who can (1) think quickly, (2) treat patients respectfully, and (3) handle complaints from the public.
Rule3. Periods go inside parentheses only if an entire sentence is inside the parentheses.
Please read the analysis (I enclosed it as Attachment A) .
The parenthesis may include:
A single word:
Thus, they remain poorly understood, and their importance is underappreciated [COCA, ACAD, 2011].
All the same, there are basic behavioral shifts that he finds can benefit many unhappy couples [COCA, MAG, 2006].
A word combination (to my regret, to my dismay/annoyance etc.):
To my disappointment, the hotel did not have an elevator and our room was on the fourth floor, we huffed and puffed all the way up the steep stairs with our heavy luggage [COCA, ACAD, 2006].
“Get your facts first, and then you can distort them as much as you please. (Facts are stubborn, but statistics are more pliable.)” 
As for Morphological aspect in the structural characteristic of parenthesis, it can be expressed in the form of:
An adverb (e.g. mostly, notably, hypothetically, probably, maybe):
Obviously, that’s a very dangerous situation [COCA, MAG, 2011].
A conjunct (e.g. therefore, or, so, hence, however, besides):
Besides, we have to be careful about trick-or-treating [COCA, FIC, 2011].
Prepositional phrase (e.g. in other words, in that case, in reality, on the contrary):
In conclusion, student teachers are educated through two approaches: 1- teaching theories before practice and 2- teaching theories while practicing pedagogically on top of field knowledge [COCA, ACAD, 2009].
Infinitive clause (e.g. to demonstrate, to sum up, to say the truth, speak frankly, to be honest):
And yet, to say the truth, reason and love keep little company together nowadays .
An -ing participle clause (e.g. putting it simply, frankly speaking):
The sole album released by a journeyman blues-rock band from Denmark in 1970, Blues Addicts is one of those records that gets its reputation for being so obscure rather than being a lost classic, frankly speaking .
Putting it simply, we felt the board was overstepping its bounds in evaluating personnel and should have deferred to the superintendent [COCA, NEWS, 1996].
An –ed participle clause (e.g. put frankly)
Completely defeated, he remained a popular leader .
Put frankly, we can resign from “isms”, welcome and support a new end of ideology [COCA, ACAD, 1990].
Some Parenthesis must be followed by a clause (Subject + verb + Object). Among them can be such words as while, why, because, so, whereas, when, etc. For example:
The quantity demanded of a good or service is inversely related to its price, whereas the quantity supplied is related directly to price, other things being equal [COCA, ACAD, 2011].
He’s been dead for 25 years, so I can only speculate [COCA, ACAD, 2011].
Other Parenthesis should be followed by a noun phrase (Cohesive word + (the) + Noun/Gerund). Some of such Parentheses are: in spite of, despite, during, because of, etc.
That’s because you weren’t able to stand the smell, so in spite of everything, you healed yourself [COCA, FIC, 2011].
Despite being fourth in the poll for most of the season, this might be one of the least talked about of Pat Summitt’s talented teams [COCA, NEWS, 2011].