This paper forms a brief and synoptic study of the use made by Greek thinkers of explanations and causes that lie outside immediate sense-perception; and of the extent to which these unperceived causes outstripped not merely sense but also common-sense, so as to become, simply judged in themselves, unexpected, improbable, or paradoxical. I propose first to examine the main Presocratic philosophers and their predecessors, to discover how far their theories exceeded the range of sense-perception on the one hand and common-sense on the other; then to assess more briefly the reaction of the Sophists, Socrates and Plato, with some consideration of Aristotle and his successors and special attention to the concept of teleology. The aim of this survey, from which much will inevitably be omitted, is to direct from a fresh angle a slender ray of light on the nature of Greek speculative thought—on the character of its dogmatism and the character of its assumed clarity.

If philosophy is the search for causes, then it must soon concern itself with the unseen, with what lies beyond perception. Proximate causes of particular sensed events may be found in other sensed events; but the philosopher's attempt to explain man's experience as a whole requires the inference of causes and relationships outside the immediate range of direct physical experience.