In June 2007 I applied for a Ph.D. to some universities for Spring 2008.Up to November 2007, I didn't get any response from these universities. This in turn motivated me to apply for fall 2008. In spite of my despair , I applied to the top universities for the fall term. Howevre,one of the spring universities ( a middle rank one) has offered me a research assitanship and I accepted the offer and actually started my research and classes. I'm very statified with my research and advisor and in my opinion it is a top class research in my area of speciality. Surprisingly , I recieved today an e-mail from MIT( the top ranked institute in my research area) that include my acceptance to the fall term!! Is it ethical to leave my current school and ignore the money which has been spent on my tuition and evenually go to MIT? I'm really confused about this. My dream was to study in such a great institute but I'm also convinced that adhering to ethics is also a very valuable thing. What do you think?What are you going to do if you were in my place?