If a list is to be evaluated as a form, the first step is to examine the first element of the list.
Special forms are generally environment and control constructs.
Every special form has its own idiosyncratic syntax. The user can create new syntactic constructs, however, by defining macros. The set of special forms in Common Lisp is purposely kept very small because any program-analyzing program must have special knowledge about every type of special form. Such a program needs no special knowledge about macros because it is simple to expand the macro and operate on the resulting expansion. An implementation is free to implement as a macro any construct described herein as a special form.