It is appropriate that a lecture in a series on ‘Philosophy and Practice’ should open by considering Bentham's ideas on imprisonment. For Bentham, incontestably a philosopher, was equally incontestably a practical reformer. This, indeed, is a received idea among philosophers; that is to say, most philosophers know that Bentham designed ‘a model prison of novel design’ (Mary Warnock), but few have actually considered the design, its implications or its effects. Most are content, like Warnock, with observing that the panopticon plan was formally rejected, before passing on to the abstraction of Bentham's felicific calculus, his notion of utility, and his ideas about the foundations of law. Yet, strange as it may seem, the underlying idea of the panopticon has never been completely abandoned. One aspect of the idea pervades penal thinking, even while prison practice is still influenced by Bentham's practical proposals; moreover, the panoptic ideal has taken root far beyond the walls of actual prisons. Here is philosophy in practice, and yet, in many ways, practically and intellectually a failure.