Relative Pronouns

Relative clauses and relative pronouns

There are two kinds of relative clauses.

    1. Defining or restrictive relative clauses are relative clauses without commas. They provide essential information about the subject or object. Here are some examples:
    2. Carbon is an element which has an atomic weight of


      A figure which has all sides equal in length is called an equilateral figure.

    3. Non-defining or non-restrictive relative clauses are relative clauses with commas. They provide additional information which can be omitted. Here are some examples:

Robotics is the study of robots, which are electro-mechanical devices that can be programmed to perform manual tasks.

An insect, which is a small animal, has a body divided into three parts: head, thorax and abdomen.

Forms of relative pronouns in relative clauses

    1. Relative pronouns relating to people
    2. -who and that are used in relative clauses when describing people

      -who and that can be used in place of noun subjects or subject pronouns. (I, you, he, etc.) and cannot normally be omitted.

      -who and that remain unchanged whether they refer to masculine, feminine, singular or plural.

      -In a defining relative clause that is interchangeable with who, but who is more common.

      e.g. a person who/that writes AI programs is usually

      a computer scientist.

      -In a non-defining relative clause only who (not that) is possible.

      e.g. Alan Turing, who wrote an article entitled

      "Computing Machinery and Intelligence" in

      1950, is considered to be the "father" of

      artificial intelligence.

    3. Relative pronouns relating to things and animals

-which and that are used in relative clauses when describing things and animals.

-In a defining relative clause that is interchangeable with which.

e.g. Many high-technology companies are involved in AI research to develop techniques which/that can improve their productivity and products.

-In a non-defining relative clause only which (not that) is possible.

e.g. Planning and decision support, which is an area of AI research, can help managers evaluate information, choose a goal, or reach a conclusion.

Notice these changes:

    1. In which/ at which can become where when describing places.
    2. e.g. There are many universities in the U.S. and other countries in which/ where AI research is being conducted.

      but Acoustics is a branch of Physics in which the properties of sounds are studied. (why not "where"?)

      Airports are places at which/ where special attention is paid

      to the weather.

      but The temperature at which water boils depends on the pressure. (Why not "where"?)

    3. By means of which can become whereby:
    4. e.g. A transducer is a device by means of which/ whereby a non- electrical signal, such as sound, light, heat, etc., is converted into an electrical signal, or vice versa.

    5. Of which can become whose

Jupiter of which the mass is two and a half times the mass of all the other planets put together is the largest planet of the Solar System.

Jupiter the mass of which is…………

Jupiter whose mass is ……………….

(The Division of English for Science and Technology,

Chulalongkorn University Language Institute)




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