1. He is a doctor of this hospital.
2. He is the doctor of this hospital.
3. He is the only doctor of this hospital.
[Does #2 mean #3? Is #2 logical? I think #1 is a common expression. Is that right?]
4. She is the principal of this school.
5. She is a principal of this school.
6. She is the only principal of this schoo.
[We can use #4, right? How about #5? #5 means that there are sevral prnicipals and she is one of them. Is this logical? Does #4 mean #6? #4 seems to be a common expression. Right?]
2 and 3 mean the same thing. We might say "at this hospital", not "of", but they do mean the same thing. 1 means he is one of potentially more than one doctor at the hospital.
#4 is best. I don't know how schools are administered in your country, but, in the USA, there is only one principal per school. There may be vice-principals in large schools, but only one principal.
In regards to your first set of sentences:
- Sentence #1: "He is a doctor of this hospital." This sentence suggests that there are multiple doctors in the hospital, and he is one of them.
- Sentence #2: "He is the doctor of this hospital." This sentence implies that there might be other doctors in different hospitals, but he is specifically the doctor of this hospital.
- Sentence #3: "He is the only doctor of this hospital." This sentence states that there is only one doctor in the entire hospital, and he is that singular doctor.
To answer your question, #2 does not necessarily mean #3. Sentence #2 implies that there could be other doctors in different hospitals, whereas sentence #3 explicitly mentions that he is the sole doctor in this particular hospital.
Sentence #1 is indeed a common expression, as it suggests that there are multiple doctors in the hospital but does not specify any exclusivity.
Moving on to the second set of sentences:
- Sentence #4: "She is the principal of this school." This sentence indicates that there is one principal in the school, and she holds that role.
- Sentence #5: "She is a principal of this school." This sentence implies that there are multiple principals in the school, and she is one of them.
- Sentence #6: "She is the only principal of this school." This sentence conveys that there is only one principal in the whole school, and she is that sole principal.
Yes, you can use sentence #4 to convey that there is one principal in the school. However, sentence #5 suggests the possibility of multiple principals, which may or may not align with the actual situation in the school. Sentence #4 does not necessarily mean #6, as #6 emphasizes the exclusivity of her being the sole principal of the school.
Sentence #4 is indeed a common expression, reflecting the presence of one principal in the school.