alumni

I'm a PNM for the fall. Do almuni have as big of an influence over rush here as they do at other big southern schools, such as Ole Miss? I read that some of the actives in the sororities had no say. Also, if you don't mind answering, how does this happen (this part is just pure curiosity)? How do the alumni have so much power if they aren't even a part of the active house anymore? Sorry for the long question, I just get really curious when I'm bored