Can anyone explain the essential difference between situations where nouns are used in a general sense and where they are used to indicate a specific type or instance of something?
Specifically, I want to understand when to use a definite article and when to use no article at all.
Murphy (fourth edition) give as an example of the specific type:
When was the telephone invented?
and as an example of the general type:
Doctors are usually paid more than teachers.
In some instances, i get a sense of why the noun is treated as it is, but not always. Moreover, in the above examples, it isn't obvious to me that the author means "telephone" exactly as a type of communication, and "doctors" may be defined as a particular profession (not in general, but rather precisely this class of workers who are paid better than others).