<p>Well, you can’t do an entire major at the other school. And you can’t take more than two classes per semester at the other school.</p>
<p>For the most part, the classes MIT people take at Harvard are either for HASS credit or for personal edification. I’m not sure about the reverse – I guess mostly Harvard science and economics people cross-register – but I suspect that in both cases, people have difficulty getting credit within their majors for cross-registered classes. They’re generally used to fill credit requirements outside the major.</p>