  Berkeley is aware that the materialist has one important card left to play: Don’t we need material objects in order to explain our ideas?  And indeed, this seems intuitively gripping: Surely the best explanation of the fact that I have a chair idea every time I enter my office and that my colleague has a chair idea when she enters my office is that a single enduring material object causes all these various ideas. Again, however, Berkeley replies by effectively exploiting the weaknesses of his opponents’ theories: