What is systematic in philosophy is its description of the world we inhabit. ‘Philosophers boast’, said Whitehead, ‘that they uphold no system. They are then a prey to the delusive clarities of detached expressions whichit is the very purpose of their science to surmount’. We need not accept Whitehead's comparison of ‘speculative philosophy’ with the systemof naturalsciences to take his point. The philosophical description of the world issystematic since ‘detached expressions’ may delude us; ‘detached’, that is, in lying outside ‘a coherent, logical, necessary system of generalideas’; we lack a conviction that they have an application to any element of our experience, which the members of a system possess, according to Whitehead, in characterizing every element. What is the nature of this system of description?