The "but" Convention

There are many calls that can be modified by "but <anything>" without further explanation. (Calls can also be modified with an explicit specification of what part is replaced, as in "Stampede but replace Trade the Wave with Cut the Diamond". Those are simple — just do what the caller says.)

For a number of these calls, one has to memorize, on a case-by-case basis, what to do. For example, on Lift Off but <anything>, the final Couples Circulate is replaced. On Line to Line but <anything> or Chisel Thru but <anything>, the final Pass In is replaced.

However, a large number of calls that take "but" modifiers follow this simple convention: the last thing that is done in the center is the thing that is replaced. Well-known examples of this are Chain Reaction, Tally Ho, and Cover Up. Less well-known examples are Link Up, Load the Boat, Square the Bases, Walk the Clover, and Make a Pass. On Percolate but <anything>, the final Hinge and Cross is replaced.