いろいろ気になったので調査.以下のようなコードを用意. module Parent CONST = 2 end module Parent module Base BASE_CONST = 3 end end module Parent module Base class Child class << self def bar puts BASE_CONST puts CONST end end end end end class Hoge include Parent::Base def fuga puts BASE_CONST puts CONST end end class Huga include Parent def baz puts CONST puts BASE_CONST end end % irb >> foo = Hoge.new => #<Hoge:0x......>