Open and Closed Forms

The concept of the open form and closed form relates to the principles of nonrestrictive clauses and is one of the few execeptions in English (US) grammar to those rules on clauses.

The value of this new rule--however dated it may seem--is that it allows sentences to 'spare the ink' so to speak when referring to such grammatical elements such as appositives.

The benefits of single word or otherwise short-worded appositives, for example, is that the meaning of the sentence is not lost or changed when removing the commas dictated by the rules of nonrestrictive clauses.

Nonrestrictive clauses call for a comma before the relative pronoun preceded by the subject or other sentence fragment preceding it. That brings us to the exception involving the open and closed form rules of grammar

Open Form

The concept of open form is quite simple and best understood by example. Though an appositive typically does not provide additional identifying information that restricts the subject it modifies; it still may avoid being enclosed by commas since the meaning of the sentence remains the same despite the exception to the most fundamental rule of grammar.

In other examples, following the same principle of the meaning not being lost, commas maybe omitted for fragments modifiying another.

With sufficient agreement among scholars, this exception has grown to earn its own definition, and as such, its opposite by virtue of necessity.

Closed Form

In simple terms, Closed Form is a reference to the strict adherence to the nonrestrictive rule, which insists on inserting commas for all clauses of a nonessential nature.

In other words, regardless of any nonambiguity, commas are always used for any sentence fragments that can safely be removed while the sentence remains true.