The difference in comma adding is the difference in restrictive relative clauses (RRC) and non-restrictive relative clauses (NRRC) – respectively the essential adjective clause and nonessential adjective clause to modify the noun (Beason & Lester, 2009).
RRC is the essential clause with no comma that restrict nouns from one group to a subgroup.
In other words, when the referent is not easily accessible to the hearer (Givón, 1993), RRC narrows and limits the meaning of the nouns by providing crucial and identifying information, and thus dissociate a subgroup from a group (Beason & Lester, 2009). Therefore, RRC cannot be omitted for accurate communication as it codes information that is necessary to the understand of the sentence (Beason & Lester, 2009).
e.g., That man with green shirt is my father.
RRC – [with green shirt]
In this situation, the speaker and hearer see a group of men. The hearer cannot accurately identify the speaker’s father from the group of men - the father is accessible but not easily accessible to the hearer. RRC comes into play at this point. The RRC [with green shirt] provides identifying and essential information to the hearer. It codes and singles out the man with green shirt from the group of men, thus successfully transmitting the idea of who is the father to the hearer.
The situation when a comma must be added in between the sentence is when the relative clause is non-restrictive in which extra and newly asserted information that is not familiar to the listener is added to the sentence.
NRRC follows and modifies a proper name or pronoun in general and here is an example:
1. Jennifer, who is Mary’s best friend, will come to the party as well.
In this case, without the adjective clause, it is still clear that Jennifer is going to the party and assumed that the fact that Jennifer is Mary’s best friend is merely a parenthetical information. To put it another way, if the information is non-essential, the clause is non-restrictive.
Compared to RRCs, more constraints are set for NRRCs. For instance, a finite head noun is required and wh-relative pronoun must be included in the clause while the use of “that” or zero relative pronoun is considered to be invalid (Arnold, 2007). Examples are as follows:
(3a) Sushi, which most Hong Kong people enjoys, is a Japanese cuisine.
(3b) * Sushi, that most Hong Kong people enjoys, is a Japanese cuisine.
(3c) * Sushi, most Hong Kong people enjoys, is a Japanese cuisine.
- Arnold, D. (2007). Non-restrictive relatives are not orphans. Journal of Linguistics, 43(2), 271-309. https://doi.org/10.1017/s0022226707004586
- Beason, & Lester. (2009). A Commonsense Guide to Grammar and Usage (5th ed.). Bedford/St. Martin’s.
- Givón. (1993). English Grammar: A Functional-based Introduction, vol. 1.. Amsterdam : John Benjamins Pub. Co.
- Syarif. (n.d.). An analysis of students’ errors in using adjective clauses.