You would’ve seen words such as because, since, after, what, who, whom, whose, that, and which at the start of dependent clauses:
We stayed home because it was raining heavily.
After she finished studying for the exam, she took a nap.
What happened at the meeting surprised everyone.
I misplaced the book that I borrowed from the library.
She met a woman whose children go to the same school as hers.
They’re marker words.
Marker words, also called trigger words or introductory words, introduce dependent clauses. The three dependent clauses – noun, relative, and adverb – are introduced by different sets of marker words, many of which overlap.
1. Noun clause marker words
1.1. List of marker words
Noun clauses are introduced by marker words that, if, whether, who, whom, whose, what, which, when, where, why, and how.
1.2. Marker words can be dropped sometimes.
When noun clause functions as direct object of verb, that can sometimes be dropped. Example:
She believes (that) he will win the competition. [You can retain or drop that.]
1.3. A marker word can be pronoun, determiner, adverb, or conjunction.
In a noun clause, marker words who, whom, whose, what, which, when, where, why, and how can be pronoun, determiner, or adverb. (Specifically, they’re called interrogative pronoun, interrogative determiner, and interrogative adverb.) Marker words that, if, and whether though are treated as subordinating conjunction. Examples:
What happened at the meeting surprised everyone. [What as pronoun]
What route we take is entirely up to you. [What as determiner]
I don’t know when the movie starts. [When as adverb]
Do you know if the meeting has been rescheduled? [If as subordinating conjunction]
1.4. Some of the marker words are clause elements.
What’s a clause element?
Elements of a clause (dependent or independent) are its basic constituents – Subject, Verb, Object, Complement, and Adverbial (SVOCA).
A marker words’ part of speech determines whether it’ll be a clause constituent or not. In other words, what we cover here flows from what we covered in subsection 1.3.
When the marker word is a pronoun, it occupies nominal positions such as subject, object, or complement. (We know that nouns and pronouns occupy nominal positions.)
What happened at the meeting surprised everyone. [What as subject of the noun clause]
They didn’t understand what the new policy entails. [What as direct object of the noun clause]
She asked me what my favorite sport is. [What as subject complement of the noun clause]
When the marker word is a determiner, it’s not a clause element. (A determiner is a part of noun phrase, which in turn is a clause element, but a determiner itself can’t be a clause element.)
What route we take is entirely up to you. [What is not a clause element, but What route is direct object of the noun clause.]
When the marker word is an adverb, it’s an adverbial.
I don’t know when the movie starts. [When as adverbial in the noun clause]
When the marker word is a subordinating conjunction, it’s not a clause element. (A conjunction – coordinating or subordinating – merely connects two clauses and is not a clause element.)
Do you know if the meeting has been rescheduled? [If is none of SVOCA.]
2. Relative clause marker words
2.1. List of marker words
Relative clauses are introduced by marker words called relative pronouns (who, whom, that, and which), relative determiners (whose), and relative adverbs (when, where, and why). (Contrary to what many resources on the internet mention, whose is not a relative pronoun.)
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2.2. Marker words can be dropped sometimes.
All but whose can be dropped under certain conditions. (Read: When relative pronoun can be dropped and when relative adverb can be dropped?) Example:
He’s the doctor (whom) I told you about. [You can retain or drop whom.]
2.3. A marker word can be pronoun, determiner, or adverb.
In a relative clause, marker words who, whom, that, and which are pronoun; marker word whose is determiner; and marker words when, where, and why are adverb. (Specifically, they’re called relative pronoun, relative determiner, and relative adverb.) Examples:
I misplaced the book that I borrowed from the library. [That as pronoun]
She met a woman whose children go to the same school as hers. [Whose as determiner]
I remember the moment when she announced her resignation. [When as adverb]
2.4. Some of the marker words are clause elements.
When the marker word is a pronoun, it occupies nominal positions such as subject, object, or complement. (We know that nouns and pronouns occupy nominal positions.)
The car that is parked outside belongs to my neighbor. [That as subject of the relative clause]
I misplaced the book that I borrowed from the library. [That as direct object of the relative clause]
When the marker word is a determiner, it’s not a clause element. (A determiner is a part of noun phrase, which in turn is a clause element, but a determiner itself can’t be a clause element.)
She met a woman whose children go to the same school as hers. [Whose is not a clause element, but whose children is subject of the relative clause.]
When the marker word is an adverb, it’s an adverbial:
I remember the moment when she announced her resignation. [When as adverbial in the relative clause]
3. Adverb clause marker words
3.1. List of marker words
Adverb clauses are introduced by a much longer list of marker words. Here are the common ones categorized under the type of adverb clause they introduce.
Note: Word enclosed in parentheses means it is optional.
Time [before]: before, until, and till
Time [during]: as, as long as, so long as, while, whilst, when, whenever, and now (that)
Time [after]: after, since, when, whenever, as soon as, now (that), and once
Place: where and wherever
Manner: as, like, as if, and as though
Reason: as, since, because, in case, and in that
Purpose: so that, so, in order that, in case, and lest
Result: so and so that
Degree or Extent: insofar as and inasmuch as
Exception: but that, except (that), excepting (that), save that, and only
Preference: rather than and sooner than
Proportion: as…(so) and the…the
Similarity: as and like
Comparison: as if, as though, like, and as
Contrast: while, whilst, whereas, and where
Concessive: though, although, even though, if, even if, when, whereas, while, and whilst
Condition: if, unless, as long as, so long as, assuming (that), given (that), in case, in the event that, provided (that), and supposing (that)
Conditional-concessive: whether…or (whether), whatever, and whoever
Contingency: when, whenever, once, where, wherever, and if
3.2. Marker words can’t be dropped.
None of the marker words introducing adverb clause can be dropped.
3.3. A marker word can only be conjunction.
In adverb clauses, all marker words are subordinating conjunction.
3.4. None of the marker words are clause elements.
Since marker words are subordinating conjunction, they’re not clause elements.
After she finished studying for the exam, she took a nap. [After is none of SVOCA.]
Since a marker word is not a clause element, what follows the marker word will always stand as a sentence (she finished studying for the exam). Contrast this with what follows the marker word in noun clause and relative clause in these sentences:
What happened at the meeting surprised everyone. [Noun clause]
I don’t know when the movie starts. [Noun clause]
I misplaced the book that I borrowed from the library. [Relative clause]
None of what follows the marker word can stand as a sentence. That’s because we’ve removed a clause element (marker word) from the clause.
