This thread links each branch and fork of the discussion, from comment, to argument, to counter argument, until the discussion reaches a dead end or is concluded. Discussions that grow mainly up have few threads, maybe only one. Discussions that grow mainly out have many interwoven threads, comprised of many digressions, tangential points, and side arguments. It is fast paced, ephemeral, and comprised of threads that can be followed one at a time in only one direction. Even when expertly moderated, such discussions can prove difficult to contribute to.
Most synchronous discussions are oral, so the life span of any one contribution is very short.
An argument, even an eloquent and powerful one, can be quickly forgotten, misunderstood, or overshadowed. While one line of reasoning is being explored, all others must be ignored. Asynchronous threaded discussion has characteristics almost opposite those of synchronous discourse. It is slow paced, perpetually transcribed, and comprised of threads that can be followed in any direction. Asynchronous on-line discussions can last from several days to several months.