Relative clause and adverb clause differ in few ways:
1. Function in sentences
1.1. Function of relative clause
Relative clause, or adjective clause, is a dependent clause that functions as an adjective in a sentence. It modifies noun phrase and usually follows it. Examples:
The person who removes a mountain begins by carrying away small stones.
The artist whose work I admire is having an exhibition next week.
This is the park where we used to play as kids.
The car that she drives is very fuel-efficient.
1.2. Function of adverb clause
Adverb clause is a dependent clause that functions as an adverb in a sentence. Being an adverbial, it answers variety of questions (time, place, manner, degree, reason, result, preference, exception, similarity, comparison, contrast, concession, condition, and more), providing background information in a sentence. You can also say it expresses variety of relationships. Examples:
When the meeting concludes, we will review the action items. [Time: The adverb clause gives information on time.]
Where the city meets the ocean, the salty breeze mingles with the urban sounds. [Place]
The company upgraded its equipment, so that production efficiency improved significantly. [Result]
The concert was enjoyable, except that the sound quality was poor. [Exception]
He handled the antique vase as though it were made of glass. [Comparison]
But for few exceptions, adverb clause can occupy more than one position in a sentence. Some of the above sentences, for example, can be written as:
We will review the action items when the meeting concludes.
The salty breeze mingles with the urban sounds where the city meets the ocean.
Relative clause and adverb clause are modifiers, implying they can be dropped and the sentence will still be grammatical. (Dropping noun clause though would result in a non-grammatical sentence.)
2. Marker words
If you noticed in the earlier examples, the two dependent clauses have been introduced by words such as who, whose, when, where, that, so that, and except that. They’re called marker or trigger words. They mark the beginning (or they introduce) the two dependent clauses.
Marker words work differently in the two clauses.
2.1. The two clauses have different set of marker words, many of which overlap.
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.) Out of these, all but whose can be dropped under certain conditions. (Read: When relative pronoun can be dropped and when relative adverb can be dropped?) Example:
The car (that) she drives is very fuel-efficient. [You can retain or drop that.]
Adverb clauses are introduced by a much longer list of marker words, with the common ones being because, as, since, before, after, until, unless, while, whereas, though, although, even though, if, when, as long as, as soon as, like, where, so that, and such that. None of them can be dropped.
The two clauses have few common marker words: when and where. Here are few examples for you to understand how they introduce two different clauses. Where the clause is adverb, it can usually be moved to front or back. Where the clause is adverb, it provides variety of background information (or expresses variety of relationships) such as time, place, manner, degree, reason, result, contrast, and condition. Where the clause is relative, it modifies a noun phrase and usually follows it. Dropping it would result in less information about the noun phrase.
When
When she finishes her work, they will go out for dinner. [Adverb clause providing information on time. The adverb clause can be shifted to end position as well.]
There will come a time when you’ll understand this better. [Relative clause. The relative clause modifies – and follows – the noun phrase a time. If we drop it, we would lose some information about time.]
Where
Where the roads intersect, there is usually a lot of traffic. [Adverb clause providing information on place]
This is the park where we used to play as kids. [Relative clause]
2.2. Marker words are different part of speech in the two clauses.
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:
The person who removes a mountain begins by carrying away small stones. [Who as pronoun]
The artist whose work I admire is having an exhibition next week. [Whose as determiner]
There will come a time when you’ll understand this better. [When as adverb]
In an adverb clause, marker words are subordinating conjunction.
In this post, we looked at the difference between relative clause and adverb clause. For difference between other dependent clauses, refer to:
