1. I have a staff who works for me.

2. I have a staff who work for me.
3. I have a staff of one who works for me.
4. I have a staff of ten who work for me.
5. I have ten staff who work for me.
6. I have ten staffs who works for me.
7. I have ten step members who work for me.
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The use of 'staff' is a little complicated. Would you check the sentences? Which ones are grammatical? Let me know the correct use of the word 'staff.' Thank you.

1 is questionable.

2-5 are just fine!

6-7 are incorrect.

Certainly! Let's check each sentence to determine their grammaticality.

1. I have a staff who works for me.
The word "staff" here is treated as a collective noun, so it can take either a singular or plural verb depending on the context. In this case, "staff" is singular and the verb "works" agrees with it. This sentence is grammatically correct.

2. I have a staff who work for me.
Similarly to the previous sentence, "staff" can function as a collective noun and take a plural verb to indicate multiple individuals within the staff. This sentence is also grammatically correct.

3. I have a staff of one who works for me.
In this sentence, "staff" is followed by the prepositional phrase "of one," indicating that there is only one person in the staff. Since "one" is singular, the verb "works" agrees with it. This sentence is grammatically correct.

4. I have a staff of ten who work for me.
Here, "staff" is followed by the prepositional phrase "of ten," indicating that there are ten people in the staff. The plural verb "work" agrees with the plural noun "ten." This sentence is grammatically correct.

5. I have ten staff who work for me.
In this sentence, "staff" is pluralized as "staff," implying that there are multiple individuals. Consequently, the verb "work" agrees with the plural noun "staff." This sentence is grammatically correct.

6. I have ten staffs who works for me.
The word "staff" is not typically pluralized as "staffs." The correct plural form of "staff" is also "staff." Additionally, the verb "works" should be changed to "work" to agree with the plural noun "staff." Therefore, this sentence is not grammatically correct.

7. I have ten step members who work for me.
The word "step members" seems to be unrelated to the word "staff" and introduces a different concept. Assuming you meant "staff members," the sentence should read, "I have ten staff members who work for me." This sentence is grammatically correct.

In summary, the correct use of the word "staff" is most often singular when referring to a group collectively, but in some cases, it can be pluralized to indicate multiple individuals within the staff.