Short Explanation and Examples:
A relative clause is a phrase that can provide more precise information about the subject in a sentence. For instance, the sentence The big dog is hungry is easily understood. However, it might be unclear if one were referring to a group of dogs. By using the sentence The big dog that I saw yesterday is hungry, the relative clause that I saw yesterday offers essential information that distinguishes a particular dog.
Relative clauses are constructed using relative pronouns and relative adverbs, as listed in the table below. The differences are further explained below.
| Relative Pronoun |
Refers to |
| that, which |
animals, objects, things, concepts, etc. |
| who, whom |
people |
| whose |
a peron or thing's posession, association, belongings, etc. |
| what |
ideas, situations, events, information, occurrences, clauses, etc. |
| Relative Adverb |
Refers to |
| when, at which |
times, time periods, etc. |
| where, in which, at which |
places, locations, areas, etc. |
| why |
reasons |
| how |
manners, ways, means, techniques, etc. |
Be careful of the following differences in relative pronoun usage.
Which versus That
Defining relative clauses provide essential information to identify the noun that they modify. They cannot be removed without changing the meaning of the sentence, and
that is usually used in these instances. Both which and that can be used in these clauses, but the meaning will change slightly if the noun is modified by the determiner
the. Specifically,
that indicates information that allows the listener to understand the use of the definite article
the, whereas
which can indicate information that allows the listener to understand the use of the definite article OR other miscellaneous information.
Please get the ball that is red.
There are probably not other red balls; the listener knows which ball the speaker is referring to
because it is red.
Please get the ball which is red.
There may or may not be other balls that are red. The listener knows which ball the speaker is referring to,
regardless of the ball's color.
Non-defining relative clauses provide additional, non-essential information about the noun that they modify. They are usually set apart by commas and can be removed without changing the core meaning of the sentence.
That cannot be used in these clauses.
OK: The class, which is taught by Professor Smith, starts at 9:00.
NG: The class, that is taught by Professor Smith, starts at 9:00.
Also, please be aware that the word
that cannot be separated from the noun that it modifies by any other words such as prepositions. However,
which can be separated.
OK: I took an interesting class in which we had to do a lot of lab work.
NG: I took an interesting class in that we had to do a lot of lab work.
Who versus Whom
Who is used when the person is the subject of the relative clause.
Whom is used in cases where the person is the object of the verb or preposition.
OK: I found a person who is willing to work on Fridays.
NG: I found a person whom is willing to work on Fridays.
The person (subject) is willing to work on Fridays.
OK: I found a person with whom I want to conduct joint research.
NG: I found a person with who I want to conduct joint research.
I want to conduct joint research with the person (object).
Also,
who should be used with quantifiers and numbers:
OK: I spoke with several people, many of whom want to conduct joint research.
NG: I spoke with several people, many of who want to conduct joint research.
Finally, please be aware of the following rules regarding relative clauses:
(1) The relative pronoun can be omitted only when it is the object of the relative clause.
OK: I wrote a paper with a researcher whom I met at a conference.
OK: I wrote a paper with a researcher I met at a conference.
I met the researcher (object) at a conference.
OK: I wrote a paper with a researcher who works with children.
NG: I wrote a paper with a researcher works with children.
The researcher (subject) works with children.
(2) The be-verb and relative pronoun can both be omitted from the relative clause if is an explanatory clause. This is especially common when the be-verb marks progressive tense (be -ing) or passive voice (be -en/-ed). However, the be-verb cannot be omitted when it is followed by an adjective.
OK: Experimentation, which is the fourth step in the scientific method, is important.
OK: Experimentation, the fourth step in the scientific method, is important.
Both of these are okay - the relative clause is
experimentation is the fourth step in the scientific method.
OK: Experimentation, which is important, is the fourth step in the scientific method.
NG: Experimentation, important, is the fourth step in the scientific method.
(3) Do not repeat the word or pronoun in the relative clause.
OK: He had to learn to use the computer that the compnay provided to him.
NG: He had to learn to use the computer that the compnay provided it to him.
The word
it refers to the computer and should not be repeated in the relative clause.