Where Terence Penelhum sees a deep continuity between John Locke's theory of ideas and David Hume's theory of perceptions, I argue that the two philosophers disagree over some fundamental issues in the philosophy of mind. While Locke treats ideas as imagistic objects that we recognize as such by a special kind of inner consciousness, Hume thinks that we do not normally recognize the imagistic content of our perceptions, and instead unselfconsciously take ourselves to sense a shared public world. My disagreement with Penelhum over Hume's debt to Locke helps to explain our disagreement over the nature of Hume's scepticism.

The state that we inhabit plays a significant role in shaping our lives. For not only do its institutions constrain the kinds of lives we can lead, but it also claims the right to punish us if our choices take us beyond what it deems to be appropriate limits. Political philosophers have traditionally tried to justify the state's power by appealing to their preferred theories of justice, as articulated in complex and wide-ranging moral theories—utilitarianism, Kantianism, and the like. One of John Rawls's greatest contributions to political philosophy has been his recognition that this is the wrong way for this field to approach its task. He points to what he calls “the fact of reasonable pluralism,” which is the incontestable fact that in a free society people striving to lead their lives ethically will subscribe to conflicting moral and religious doctrines, many of which will be “reasonable” in the special sense of leaving their adherents willing to cooperate with those with whom they have moral disagreements. And this means that political philosophers can no longer rely on any particular “comprehensive” doctrine in their attempts to justify the state. For doing so would be unfair to those who subscribe to a conflicting reasonable doctrine; it would mean that the coercive power of the state would not be justified to them in terms they can accept, even while they were forced to abide by its terms.