  But why?  The closest Berkeley ever comes to directly addressing this question is in his early philosophical notebooks, where he observes that “Two things cannot be said to be alike or unlike till they have been compar’d” (PC 377). Thus, because the mind can compare nothing but its own ideas, which by hypothesis are the only things immediately perceivable, the representationalist cannot assert a likeness between an idea and a non-ideal mind-independent material object. (For further discussion, see Winkler 1989, 145–9.)