Hi Mikkel, I think it is simply because "not" is not a method, but instead a pure operator. (For example, see Table 18.4 in the Pickaxe book). (Well, although Ruby is pure OO, it still has both methods and operators.) Regards, Bill ========================================================================== MikkelFJ <mikkelfj-anti-spam / bigfoot.com> wrote: > Why is the following not valid: > (some boolean expression).not > true.not > Mikkel