x = 1 # This is the value we're working with
x.is_a? Fixnum # true: x is a Fixnum
x.is_a? Integer # true: x is an Integer
x.is_a? Numeric # true: x is a Numeric
x.is_a? Comparable # true: works with mixin modules, too
x.is_a? Object # true for any value of x