Many elements separated by commas or dashes are either insertions or appositives. They provide supplementary information that does not affect the sentence structure (SV), so temporarily removing them makes the overall structure easier to see.
Basic Rules
Insertion: A phenomenon in which independent information (adverbial notes, the speaker's opinion, or connective phrases) is inserted in the middle of a sentence and enclosed by commas or dashes.
- Adverbial insertions: however, / for example, / in fact, / as a result,
- Participial construction inserted: The theory, developed in the 1990s, remains influential today.
- Nonrestrictive use of a relative clause: Dr. Smith, who led the study, later published the results.
Apposition: An element that restates or specifies the noun immediately before it in different words.
- Noun + noun: the fact that 〜 / the idea that 〜 / the belief that 〜 (the that-clause is appositive)
- Apposition with commas: Tokyo, the capital of Japan, hosts millions of visitors each year.
- Apposition with of: the problem of overpopulation
It is especially important to determine whether that introduces an appositive clause or a relative clause: if the preceding noun is an abstract noun with content such as “fact / idea / belief / possibility / news,” and what follows that is a complete sentence, the clause is appositive. If the preceding word is an ordinary noun and what follows that is an incomplete sentence (with a missing subject or object), it is a relative clause.
The theory, first proposed in the 1960s, is still debated among scientists. (The theory was first proposed in the 1960s, but it is still debated among scientists.) ← Participial construction inserted
The fact that the medicine had side effects was not disclosed to patients. (The fact that the medicine had side effects was not disclosed to patients.) ← that-clause = appositive (the content of the fact), followed by a complete sentence
The medicine that caused the side effects was later withdrawn from the market. (The medicine that caused the side effects was later withdrawn from the market.) ← that-clause = relative clause (modifying the medicine), followed by an incomplete sentence lacking a subject
Kyoto, once the capital of Japan, still attracts historians from around the world. (Kyoto, once the capital of Japan, still attracts historians from around the world.) ← Apposition (Kyoto = the former capital)
Points to Note
① When you temporarily remove an insertion and read the sentence, its structure often looks surprisingly simple. “The theory (, first proposed in the 1960s,) is still debated.” → “The theory is still debated.”
② Check for an appositive that-clause: if everything necessary, such as “S+V+O,” is present immediately after it (a complete sentence), it is appositive; if S or O is missing (an incomplete sentence), it is a relative clause. This grammatical check is the most reliable.
③ Nouns that commonly take appositives: fact / idea / belief / possibility / news / rumor / assumption / evidence / claim. When a that-clause follows one of these, first suspect apposition.
④ When an insertion is long, overlooking the comma or dash marking its beginning and end can lead you to mistake a noun within the insertion for the subject or object of the entire sentence. It is important to identify the exact range of the insertion.
- Temporarily remove insertions and appositives to read the sentence structure
- Appositive that-clause: followed by a complete sentence and occurring after fact/idea/belief, etc.
- Relative that-clause: followed by an incomplete sentence (with a missing element)
- Apposition with commas: restates or specifies the preceding noun
- Identify the exact beginning and end of an insertion (commas or dashes)
Practice
- Determine whether that in the following sentence is appositive or relative, and explain why: The belief that hard work always leads to success is not always true.
- Put the insertion in the following sentence in parentheses and show the sentence structure: The experiment, conducted over five years, revealed unexpected results.
- Name three nouns that commonly take appositives.