: For millions of people, text-based computer-mediated communication (CMC) is a convenient and engaging way to exchange information and opinion. Research shows that the social ambiguity of text-based CMC, such as email, can both promote participation and group cohesion and lead to misunderstanding, offence and social division. We report a field experiment that attempted to expose some underlying factors. GNU Mailman was configured to promote either individual or group perspectives during email discussions. It was used for political debate by two groups of Indonesian NGO members during the Indonesian constitutional crisis of