Coordinating Conjunctions (FANBOYS), Correlative Conjunctions, and Compound Sentence Construction

The Seven Coordinating Conjunctions (FANBOYS) and Their Logical Functions

Coordinating conjunctions are structural words used to join grammatically equivalent elements—such as two single nouns, two verb phrases, two prepositional phrases, or two complete independent clauses. Traditional school grammar groups seven coordinating conjunctions under the mnemonic FANBOYS: For, And, Nor, But, Or, Yet, and So.

Each coordinating conjunction expresses a distinct logical relationship between the elements it connects. Selecting the appropriate conjunction requires identifying how the second thought relates to the first:

Punctuation Rules: Compound Sentences vs. Compound Predicates

A core coordination skill is determining whether to place a comma before a coordinating conjunction. This decision depends entirely on the syntactic structure of the second element being joined.

1. Compound Sentences (Two Independent Clauses) → Comma Required

A compound sentence consists of two independent clauses linked by a coordinating conjunction. An independent clause contains both a subject and a finite verb and can stand alone as a complete sentence. For formal multiple-choice items, the standard default is a comma immediately before a coordinating conjunction that joins two independent clauses. Some style guides permit omission between very short, closely linked clauses, but do not assume that exception unless the item clearly establishes it.

• Formula: [Independent Clause 1] + , + [FANBOYS Conjunction] + [Independent Clause 2]
• Correct Example: The laboratory technician calibrated the microscope*, so** the optics provided clear images.*
• Analysis: Both sides of so are complete clauses: The laboratory technician calibrated the microscope (Subject: technician, Verb: calibrated) and the optics provided clear images (Subject: optics, Verb: provided). The comma before so is mandatory.

2. Compound Predicates / Verbs (Single Subject, Two Verbs) → No Comma

A compound predicate occurs when a single subject performs two or more actions joined by a coordinating conjunction. Because the second verb shares the subject from the first part of the sentence and does not introduce a new independent clause, no comma should precede the conjunction.

• Formula: [Subject] + [Verb 1] + [FANBOYS Conjunction] + [Verb 2]
• Correct Example: The laboratory technician calibrated the microscope and examined the biological samples.
• Incorrect Example (Comma Error): The laboratory technician calibrated the microscope*, and** examined the biological samples.*
• Analysis: The phrase examined the biological samples lacks its own explicit subject. The noun technician serves as the subject for both calibrated and examined. Placing a comma before and in this compound predicate structure is a punctuation error.

3. Subject-Auxiliary Inversion with Nor

The coordinating conjunction nor carries unique syntactic behavior. When nor connects two negative independent clauses, the second clause undergoes subject-auxiliary verb inversion (the auxiliary verb or modal moves before the subject, exactly like a question structure).

• Standard Negative Structure: She did not attend the meeting. She did not send a surrogate.
• Combined with Nor: She did not attend the meeting, nor did she send a surrogate.
• Notice the Inversion: Following nor, the auxiliary verb did precedes the subject she, followed by the base verb send. Failing to invert the subject and auxiliary verb after nor (for example, nor she sent) is a frequent error on ESL placement exams.

Correlative Conjunctions and Parallel Structure Rules

Correlative conjunctions are paired conjunctions that work together to join grammatically equal sentence elements. Because they function in pairs, they require precise structural symmetry.

High-Frequency Correlative Pairs

• Both ... and (expresses addition of two elements)
• Either ... or (expresses a choice between two positive alternatives)
• Neither ... nor (expresses a choice between two negative alternatives)
• Not only ... but also (expresses emphasis on an additional element)
• Whether ... or (expresses alternative conditions or possibilities)

The Rule of Parallel Structure (Parallelism)

The cardinal rule governing correlative conjunctions is parallelism: the grammatical construction that follows the first conjunction must match the grammatical construction that follows the second conjunction. If a prepositional phrase follows not only, a prepositional phrase must follow but also. If an infinitive verb follows either, an infinitive verb must follow or.

Subject-Verb Agreement with Correlative Conjunctions

When correlative pairs such as either...or and neither...nor join two subjects of different grammatical numbers (singular and plural), the verb must agree in number with the subject closest to the verb (the proximity rule):

• Singular + Plural Subject: Neither the lead researcher nor the laboratory assistants were able to replicate the outcome. (Plural verb were agrees with plural assistants).
• Plural + Singular Subject: Neither the laboratory assistants nor the lead researcher was able to replicate the outcome. (Singular verb was agrees with singular researcher).

Worked Examples and Sentence-Combining Applications

On the ACCUPLACER ESL Language Use test, sentence-combining items evaluate your ability to join short, choppy sentences into a single, syntactically sound compound sentence.

Exam Strategy: Identifying Coordination Flaws

Consider the following pair of choppy sentences:

• Original Sentences: "The department chairperson approved the course revision. She did not authorize additional funding for new equipment."
• Option Assessment:
  1. Unflawed Combination: "The department chairperson approved the course revision**, but** she did not authorize additional funding for new equipment." (Correct: Places a comma before the contrasting coordinating conjunction but joining two independent clauses).
  2. Flawed Combination (Comma Splice): "The department chairperson approved the course revision, she did not authorize additional funding for new equipment." (Incorrect: Lacks a coordinating conjunction between the independent clauses).
  3. Flawed Combination (Missing Comma): "The department chairperson approved the course revision but she did not authorize additional funding for new equipment." (Incorrect: Omits the required comma before but when connecting two independent clauses).
  4. Flawed Combination (False Compound Verb Comma): "The department chairperson approved the course revision, but did not authorize additional funding for new equipment." (Incorrect: Places an unnecessary comma before but when joining a compound predicate without a second subject).