A debate is live. Therefore it requires that more than one person is connected at the same time.
Seminars can happen over a period of time.
You would use a debate as a less formal opportunity to discuss with fellow students and tutors a particular topic. To participate in the live discussion it is not expected that you can verify an opinion, instead it is hoped that you will respond to the live conversation with ideas and thoughts as they occur to you. There are various Internet Chat systems around. The system used here is deliberately simple and not sophisticated. This is because we recognise that many people who use Whitehall On-line are new to the Internet.