Whitehead is faced with the problem how, if according to the physicist the physical world consists of atomic activities, we nevertheless perceive it as made up of such common sense objects as trees, houses, tables, etc., which have a continuity about them. He notes, for example, the difference between the paving stone as perceived visually and its physical molecular activities. Pragmatically, he tells us, a paving stone is a hard, solid, static, irremovable fact. But this, he goes on, is a very superficial account if physical science is correct. Our sense-experience would then seem to omit any discrimination of the fundamental activities within physical nature.¹