How to use "of" "at" "with" "from" etc. to explain where a person belongs to? My english is not so well, so the title I wrote may be a little confused. When I was reading some articles, I've seen some sentences as follows: 1. Dyann Wirth is the head of infectious diseases [at] the Chan School of Public Health [at] Harvard. 2. Students [at] the University of Colorado 3. Jamie Merisotis [of] the Lumina Foundation 4. Rakesh Kochhar is an economist [at] the Pew Research Center 5. Heather Boushey, [with] the Washington Center for Equitable Growth I presume these prepositions indicate the place or organization that a person belongs to. But sometimes it uses "at", sometimes it uses "of" or "with". Sometime I see "from" is used, but I can't find the example. I failed to figure out how to use these prepositions. Does it depend on the size of the institution? I hope I have made myself clear. I will be appreciated if you could give me some answers. Thank you!!