In Foulkes the concept of matrix is closely connected with a social theory of mind and thus the unconscious, which stands in contrast to the metapsychology of classical psychoanalysis. However, Foulkes only partially succeeds in explicating this social theory of mind and using it for a group-analytic concept of the dynamic unconscious. The intersubjective change in psychoanalysis opens up a new window of opportunities for that. Possible consequences for the understanding of consciousness and the unconscious within a group are outlined in the first part of the following article. Among these consequences is the awareness of the central role of the play or play-block in establishing shared consciousness or unconscious. This significant meaning of play for the group-analytic process is explained in detail in the second part. The playful nature of the group-process, containing emotional presence, freedom from specific purpose and the simulation of real-life situations, develops in the protective atmosphere of clearly defined settings. This is basic to a creative group process where an as-if-situation gives room to perform and re-arrange patterns of relations. Here, conscious processes mesh with unconscious ones. Finally, specific situations in plays are presented to illustrate the significance of the sensory-symbolic level of communication for the group's mentalization process.