Introducers that and wh-Words and Phrases
A relative clause can begin with one of the following kinds of relative clause “introducer”:
1. the word that
2. a “wh-word” such as who, whom, or which
3. a “wh-phrase” that begins with whose or that includes one of the wh-words in #2.
Examples of #3 are whose camera, to whom, and from which. The following sample sentences illustrate these options:
A scanner is a device that allows you to convert an image to a digital format.
A scanner is a device which allows you to convert an image to a digital format.
A scanner is a device with which you can convert an image to a digital format.
A scanner is a device that allows you to convert an image to a digital format.
The photographer whose scanner I borrowed asked me to return it.
The photographer from whom I borrowed a scanner asked me to return it.
The photographer who I borrowed a scanner from asked me to return it.
The photographer that I borrowed a scanner from asked me to return it.
No Introducer
A fourth option for introducing a relative clause involves neither that nor a wh-word or phrase. In such cases, the relative clause has no introducer as in the sentences below.
The photographer I borrowed a scanner from asked me to return it.
There are many things you can do with a digital camera.