Senators holding discussions on the Senate floor during a quorum call. Click on picture for larger image

There are four primary reasons for these unpredictable extended quorum calls in the Senate. Unfortunately, musical interludes is not one of them. Neither is the usual definition of a quorum -- to obtain the presence of a majority on the floor.

Instead, their purpose is to give the Senate a way to hold a "constructive delay." While the clerk slooowly calls the roll, Senate floor activity is temporarily suspended. This give Senators the opportunity to either (1) negotiate a deal "off-stage", (2) await the arrival of a "missing" Senator who was promised the chance to offer an amendment or make a floor statement; (3) take hostility off the floor and settle it in the cloakrooms ("duking it out" House-style, verbally or physically, is not Senate practice) or (4) buy some time to figure out the procedural counter-move when surprised by an amendment or procedural motion.

When Senators need to seek a temporary delay in the floor proceedings, the only alternative to a quorum call is to move to recess or adjourn. Both have varying procedural consequences best avoided, e.g. displacing the pending business. Moreover, only the Majority Leader or his designee may offer motions to recess or adjourn, a restriction established by tradition to protect the Leader's control over the Senate's schedule. When a delay is needed, it is not always timely to go hunt for the Leader. So, quickly suggesting the absence of a quorum is both a more practical, as well as procedurally safer, method.

When the need for the delay has ended, any Senator ready to resume business asks the Chair to "rescind," or withdraw, the quorum call. This takes unanimous consent. If there is no objection, floor action resumes and the quorum call ends. It is considered "vitiated," or undone. The quorum call is not officially recorded. It's as if it never happened, so no Senator's voting record reflects his/her failure to respond.

Now, what if a Senator truly wanted to gather a majority together and really get a quorum to the floor? He or she would make a "motion to instruct the Sergeant-at-Arms to request the attendance of absent Senators," otherwise known as a "live quorum."