  This is an intuitive introduction to classic sliding mode control that shows
how the associated assumptions and condition for its use arise in the context
of a derivation of the method. It derives a controller that obviates the need
for the assumption of any sign for the control input vector, answers why it is
said that it deals only with matched disturbances and why a system that it may
apply to 'must' be linear in the control signal. Additionally, it may be viewed
as an example of how a control design method might be developed, adding to its
pedagogical usefulness.
