1.219 using individuals to generalize

You can use 'a' or 'an' with a noun when you are using one individual person or thing to make a general statement about all people or things of that type. For example, if you say 'A gun must be kept in a safe place', you are talking about an individual gun in order to make a general statement about all guns.

• A computer can only do what you program it to do.
• A dog likes to eat far more meat than a human being.
• An unemployed married farm-worker got parish relief.

This is not the usual way of referring to groups. Normally, if you want to make a statement about all the people or things of a particular kind, you use the plural form of a noun without a determiner. See paragraph 1.212 for more information about this.