Linguistic Overview
Complex sentences work by embedding one clause within another. Embedded clauses serve a particular grammatical function within the host clause (acting much like a part of speech): Adverbial and Relative Clauses serve the role of modifiers, while Content Clauses serve the role of nominals.
It’s possible to have two or more embedded clauses in the same host clause (as in, “The robot will continue working until you tell it to stop, unless it runs out of battery.”) or to even have one embedded clause nested inside another embedded clause (as in “Francine told me that whoever stole her lunch is in big trouble!”). There is no limit to how many embedded clauses a sentence can hold.
Structure
Host Clauses
A host clause is any clause that has an embedded clause within it.
The Main Clause
The main clause forms the base of a sentence, and it is not embedded within another clause. The main clause determines the purpose and mood of the overall sentence. For instance, if a sentence is intended to be a question, then the main clause must take on an interrogative structure (by contrast, an interrogative subordinate clause inside a declarative main clause does not make the sentences as a whole interrogative).
Another common term for main clauses is independent clauses. However, this is a misnomer as they sometimes rely their embedded clauses to complete their meaning, and occasionally to even complete their grammatical structure (see the ‘Essentialness’ section for details). Therefore, Insights to English avoids the terms dependent and independent when referring to clauses.
In complex sentences, all subordinate clauses are ultimately embedded within the main clause, whether immediately so or by embedding inside another subordinate clause between.
Embedded Clauses
An embedded clause is a clause that fits inside another clause (which is its host clause). While it might seem as if a subordinate clause is next to its host clause by occurring at the beginning or the end (where Adverbial Clauses are often found), they are actually inside the host clause in a similar way to how adverbs, prepositional phrases, and myriad other elements are part of a greater clause.
Every subordinate clause in a complex sentence is an embedded clause.
Subordinate Clauses
A subordinate clause is a clause that, by design, cannot be the main clause of a sentence (which also means it cannot be regarded as a sentence all on its own). Rather, subordinate clauses play a particular role within their host clause, just like any part of speech.
- Adverbial Clauses serve as modifiers (like adverbs) and can modify virtually any part of the main clause.
- Relative Clauses are also modifiers, usually modifying nouns (like adjectives do).
- Content Clauses serve as nominals (like nouns) and can therefore be subjects, objects, or predicative nominals.
At the front of each subordinate clause is a subordinating conjunction. Each type of subordinate clause has its own set of possible conjunctions.
Linkers
Subordinating conjunctions — also called subordinating linkers or simply subordinators — introduce subordinate clauses and link them to their host clause. There are three sets of subordinators, one for each type of subordinate clause:
- Adverbial subordinators introduce Adverbial Clauses. There is a wide variety of adverbial subordinators to account for the various ways a grammatical element can be modified.
- Relative linkers (or relativizers) introduce Relative Clauses. What makes them special is that these linkers have dual roles: not only are they conjunctions, but they also act like pronouns referring back to a key noun from the host clause.
- Cruxes (or complementizers) introduce Content Clauses. These play a pivotal role in their sentences both functionally and semantically because they often embody the central concept that the host clause points toward.
The specific subordinator that is used determines the purpose and meaning of its subordinate clause. For instance, ‘because’ and ‘until’ are both adverbial subordinators, but the first is about cause and effect while the second is about timing. Similarly, ‘whether’ and ‘where’ are both cruxes, but the former challenges the reality of a situation while the latter prompts details about a location.
Types of Subordinate Clauses
Adverbial Clauses
Adverbial Clauses are very similarly to prepositional phrases in how they can modify almost any other part of a sentence. A key difference, however, is that unlike prepositional phrases, Adverbial Clauses are, of course, complete clauses.
- role: modifiers (usually modify verb phrases or even entire clauses, but can also modify noun phrases)
- linkers: a long list of adverbial subordinators convey a range of meanings, including Comparison, Condition, Concession, Location, Manner, Purpose, Reason, Result, and Time
- placement: go before, after, or within whatever element they are modifying; alternatively, can come after a linking verb when modifying the subject
- essentialness: usually either non-restrictive or arguments, but can be restrictive
Relative Clauses
Relative Clauses share a key element (a word or phrase) with their host clause. In the host clause, that element is either a noun phrase or the entire clause. Relative Clauses are a way to share more information about that key element within the same sentences as the main clause.
- role: modifiers, typically of nouns (but sometimes of entire clauses)
- linkers: relativizers include ‘WH’ Words along with ‘that’; the particular relative linker depends upon what part of speech the key element is used as within the Relative Clause, and on whether the Relative Clause is restrictive; relativizers aren’t just linkers, but also play a semantic role in their clauses
- placement: go immediately after the key noun in the host clause
- essentialness: either restrictive or non-restrictive
Content Clauses
Content Clauses are noun phrases that are made up of entire clauses. As such, they can be the subject, direct object, or predicative nominal of a sentence.
- role: nominals
- linkers: the most common cruxes are ‘WH’ Words, ‘whether’, ‘if’, and ‘that’; they tend to be the focal point of both the Content Clauses and their host clauses
- placement: go wherever a noun or pronoun would go within the host clause; most commonly, as verb complements (direct objects), they come right after the host clause’s verb
- essentialness: arguments
Advanced Concepts
Essentialness
Subordinate clauses have three levels of essentialness:
- grammatically essential to the sentence → These are called arguments.
- not grammatically essential, but essential to the meaning of the sentence → These are restrictive adjuncts.
- not essential to the sentence at all → These are non-restrictive adjuncts.
Arguments
Arguments cannot be removed from the sentence. Content Clauses are typically arguments. For the example “I’ll take whatever tools you have available,” if you remove the Content Clause then all you have is “I’ll take.” But since take is a transitive verb and needs a direct object, the main clause “I’ll take” is not a complete sentence by itself.
Adverbial Clauses that serve as predicative modifiers (meaning they follow linking verbs) are also arguments. If you remove the Adverbial Clause from “These new rules are because accidents have increased in the last quarter,” then you are left with “The new rules are,” which is not a complete sentence.
Restrictive Adjuncts
The opposite of an argument is an adjunct. Adjuncts are parts of sentences that can technically be removed. However, if restrictive adjuncts were to be removed, the sentence would lose essential meaning.
Relative Clauses can be restrictive, as in “This is the spot where the couple had their first kiss.” If we remove the Relative Clause, we’re left with “This is the spot,” which is grammatically correct sentence, but one which makes no sense without further context.
Less commonly, Adverbial Clauses can be restrictive. For example, the Adverbial Clause in “Caroline have more experience than Devin has,” completes the idea of the comparative introduced by ‘more’ in the main clause.
Restrictive modifiers typically define or specify whatever they’re referring to.
Non-Restrictive Adjuncts
Non-restrictive adjuncts can be removed from the sentence without it losing critical information. Instead of defining or specifying, they merely describe their referents.
Both Relative Clauses and Adverbial Clauses can be non-restrictive. Consider the examples, “Let me introduce you to Archie, who designed this skyscraper,” and “We cancelled the trip because the storm came on so quickly.” If we were to remove the subordinate clauses, we’d be left with “Let me introduce you to Archie,” and “We cancelled the trip.” The lost information might have been helpful, but they weren’t essential to understand the meaning of these sentences.
Non-restrictive Relative Clauses need punctuation (usually commas) before and after to set them apart from their host clauses. Non-restrictive Adverbial Clauses sometimes need commas after to set them apart, especially if they are long clauses. By contrast, restrictive clauses need no punctuation to set them apart.
Complex Complex Sentences
It’s possible to embed a subordinate clause inside another subordinate clause, which in turn is embedded inside a third clause. In fact, there might be even more than three levels of clauses, though this is rare in modern English. But suppose we have a structure like this:
Main Clause [ Subordinate Clause 1 [ Subordinate Clause 2 ] ].
That middle clause (Subordinate Clause 1) is an embedded clause because it is inserted inside the main clause. But the middle clause is also a host clause because it has Subordinate Clause 2 nestled inside it.
Here’s what to remember:
- Every subordinate clause is an embedded clause, and every embedded clause is a subordinate clause. However, some subordinate clauses are also host clauses.
- Every main clause is a host clause. But not every host clause is a main clause, as it’s possible for subordinate clauses to also be host clauses.
Also keep in mind that any host clause may have more than one embedded clause.
Non-Finite Clauses
Clauses require finite verb forms (the present basic, the -s form, or the past form) that are in agreement with their subjects. Non-finite verb forms (infinitives and participles) cannot be the main verbs of their clauses.
Some resources refer to certain grammatical structures as ‘non-finite clauses’. Some examples may be: “I refuse to meet with that heinous man,” or “Imagine yourself sitting upon an elegant throne.” However, these bolded phrases cannot stand alone, nor do they have any linkers. Insights to English considers ‘non-finite clauses’ to be a misnomer and regards the examples here to be phrases, but not clauses.
See the Infinitive Phrases page or the Participial Phrases page for more information.
Subjunctive Verb Phrases
When subordinate clauses are in certain types of unreal mood — usually hypothetical — they might feature subjunctive verb phrases.
There are two types of subjunctive:
- Verbs are limited to only their base form or their past simple form, as in “I expect that you arrive on time,” or “If I were you, I’d reconsider.” There are no ‘s suffixes or -ing forms for these subjunctives.
- Subject-auxiliary inversion is used, even for declaratives, as in “She wouldn’t have done that had she known better,” or “Should you need anything, I’ll be in my office.”
Subjunctives are most likely to be found in Conditionals. But subjunctive verb phrases are considered to be very formal and are not commonly used, so most English learners might rarely if every encounter them.
Subjunctives can only apply to subordinate clauses, never main clauses.
Further Reading
| Related Concepts | Applied Grammar Topics |
|---|---|
Complex Sentences
Basics
Types of Subordinate Clauses
Adverbial Clauses
Comparison • Concession • Condition • Manner • Time & Place • Purpose, Reason, & Result
Content Clauses
Indirect Speech {Reported Speech • Indirect Questions} • Cognitive Expressions • Relief, Regrets, & Reprimands
