INTRODUCTION The first step in understanding any science is to learn its language. Like other specializations, technical theater has a unique vocabulary incomprehensible to most lay people. Blank stares and puzzled looks are common reactions when a technician discusses very simple items such as "flats," "keystones," "crosbys," etc. These terms are not hard to understand once they've been defined. Structural design, like technical theater, has its own specialized vocabulary, one which is not especially difficult to understand, and which makes the discussion of ideas easier by assigning names to well-understood concepts. This vocabulary lets structural designers get to the root of a problem without getting lost in trivial details.