Why do people omit the definite article?

I'm used to always hearing or seeing a definite article before certain nouns. Yet on certain occasions the article is totally omitted, and it bothers me. I'm wondering what the justification for omitting the article is, especially when the definite article would seem to be required, or if it is just bad English either on the part of the individual in question or more likely by tradition.

The most frequent place I hear this is at the doctor or dentist's office. In every one I have ever visited, the receptionist or assistant always says things like "Doctor will see you shortly" instead of "The doctor will see you shortly."

The wikipedia article linked above says this: "A definite article indicates that its noun is a particular one (or ones) identifiable to the listener". In the case of a clinical setting, I know who the doctor is, especially if this is not my first visit. The people in the office know the doctor even better than I, so it would seem to be inappropriate to omit the article. Even the indefinite article would be incorrect. It further says, under "Zero article": "In languages having a definite article, the lack of an article specifically indicates that the noun is indefinite." Since the noun is not indefinite, why are they omitting the article?

Another place I see the article omitted is with the word "bar". Bartenders apparently don't say "I tend the bar" they say "I tend bar". Unless a bartender works in multiple bars, it would seem like an article would be required. Furthermore, "the bar" can mean any bar a person goes to, so even in a case like this question, it seems like the word "the" should be in the sentence. The only thing I can think of in this case is maybe the speaker doesn't want to confuse the listener into thinking they work in the legal field.

Is this just a bad habit, a historical corruption or tradition, or is there really a valid reason (or perhaps more than one) for these omissions?

Answer

In the first example, Doctor is being used as the name of the person; the doctor is more of a descriptive phrase. It's short for Doctor .

tend bar is a set phrase, it's a synonym for being a bartender. It's also similar to the way other people describe their work: a mailman could say I deliver mail, a programmer would say I write code, a garbageman would say I collect garbage, and a composer would say I write music. These are all using the noun to refer to the general concept, rather than any specific item, so no article is needed. You would add an article when you need to be specific, e.g. I write the music in TV commercials.