all staff，all staffs
Hello，Everyone！！
I don't know if I should pick a plural noun behind ”all” or singular in the following two sentences：

The management has assured -------all staff -----that anyone attending the professional development seminars will receive a certificate thanking them for their participation.

The management has assured -----all staffs-----that anyone attending the professional development seminars will receive a certificate thanking them for their participation.

Thanks very much in advance ！

Question

all staff，all staffs
Hello，Everyone！！
I don't know if I should pick a plural noun behind ”all” or singular in the following two sentences：

The management has assured -------all staff -----that anyone attending the professional development seminars will receive a certificate thanking them for their participation.

The management has assured -----all staffs-----that anyone attending the professional development seminars will receive a certificate thanking them for their participation.

Thanks very much in advance ！

Answer

Thank you very much，Celeste！！！！！：）
Thanks for your helping with my English learning

Answer

The reason why it's "all staff" is because "staff" is a collective noun; it refers to a group. Saying "staffs" is like saying "groups." That implies that there are multiple staffs. "All" refers to everyone in a particular group, so everyone in the staff.

Answer

ahhh，I got it ！！！

Answer

why？is there any reason for that？

Answer

The correct expression is 'all staff'