Reason--let me repeat--is the imaginary extension of experience by comparison with more complete experience of a similar kind. By reasoning in inherence we complete single objects; by inference in association we complete groups. These two categories demonstrate that a natural group consists of fragments of objects, and fragments of other natural groups which are possible but not yet developed. A hill is partly concealed by a house, the house partly concealed by a tree, the tree by a stone fence, the fence by a growth of ivy. A river disappears at a curve and is lost to view; we know from experience of other rivers that under certain conditions we might perceive the river further on as a feature in several more landscapes. As we gaze at an association of objects these possible completions occur to us--not fully or definitely but sufficiently to convince us that the group might be developed into many other groups, and into a multitude of objects of forms different from those we actually perceive. By our hypothesis the observer has always been stationary, the objects have moved to and fro but not from near to far. Their real dimensions have remained unaltered, and nothing has occurred to suggest that they ever appear of other dimensions. In short we are gazing on a piece of stage-scenery. But there is another element in perception. We and all other real (mental) beings are part of the cosmic force. We are co-creators of what we perceive--limited gods, not machine-men as the scientific people would have us believe. But for our power of affecting each other and our readiness to receive impressions from other minds, there would be no perception--no material objects. We (that is, all sentient beings) could, by unanimous resolution, annul the material creation--blot out the universe of objective things in a moment. United to and implied in this general power is the particular power of modifying our world without destroying it. We can redistribute the active and passive forces so as to produce other perceptual effects than those present at a given moment. And we habitually do this to some extent. Within a limited scope our world is plastic as dough, and we knead it to any form we please. For example, we exert energy to change our place, and immediately the group before us breaks up and undergoes metamorphosis. Some objects disappear altogether, and entirely new objects present themselves. Some become smaller, others larger; some fractional forms fill out to completion, some integers undergo curtailment, others separate into several distinct objects. In a few minutes the first group has dissolved into a second, which may merge into a third, and so on indefinitely. In contemplating these phenomena we discern a third form of completeness and incompleteness, distinct from those that enter into inherence and association. Hence a new type of reasoning--another category: the Perspective.