The episode of collective thinking represented by Sequence 3.2 was built on the foundations of the common knowledge of the participants. Several different kinds of common knowledge were involved. The first and most obvious is their common experience of having watched the film E.T. They all began the activity with at least a basic shared understanding of the main topic and the purpose of their talk, and so could create a shared frame of reference for their activity and make sense of what was said-even if the information they went on to provide was not always made very explicit. The second kind of common knowledge on which their talk drew was past experience of doing ‘collective remembering’, because this is a common human pursuit. They would all be likely to be familiar with an appropriate set of conversational ground rules for carrying out this kind of joint intellectual activity. Both these kinds of common knowledge are to some extent apparent to us (as observers) in the content of the talk, and they contribute to the fluency of the interaction. So, though the students may all have seen the film on separate occasions, and may never have engaged in collective remembering together before, they nevertheless have a great deal of relevant cultural knowledge in common. A third kind of common knowledge on which the students could probably draw would be past joint activity. Being a group of students who were all following the same course, they may have worked together before, and so have a history of shared activity and personal relationships which are acted out in this conversation. So this activity may, at least for some of the participants, have been an episode of the ‘long conversation’ of their personal relationships. And, as the conversation unfolded, they had the resources of the history of their continuing joint activity on which to draw. So when Lesley said: ‘and what’s that little girl that he fancies’, she was assuming, quite reasonably, that the others would know that ‘he’ referred to the character Elliott rather than to E.T. The common or given knowledge on which we draw in order to think together may therefore be of several different kinds.