When MOOCs are increasing all over the world as a mean for improving the diffusion of culture and science, it is interesting to observe how those MOOCS build communities of knowledge, and which is the impact of those communities on the acquisition of knowledge. In this article, we present the principles of design of the MOOC Digital & Culture Writing that aims to spread digital culture. Then, we analyse the messages posted on forums by the related community, and the cognitive process to which they refer. Posts analysis reveals reflexivity processes when participants are writing on forums. It appears that reflexivity cognitive processes are at the heart of both social interaction and digital culture acquisition.