Science constantly confounds sequence and causation. We are told that the moon _causes_ eclipses of the sun, that heat _causes_ objects to expand, that a seal _causes_ an imprint. This is a metaphor from human causation, and the expression is now so rooted in language that it would hardly be possible to introduce a more correct phraseology. Yet it is as incorrect as to say that one o'clock causes two o'clock, or that daylight causes darkness. The confusion has arisen from the fact that both sequence and causation deal with fixed inconvertible series, but only in the latter is there real power exerted to produce the effect. Material things and their apparent effects are due to a cause lying behind both. XXVII--CAUSATION Causation differs from all other categories in that one of its elements is mental. It is a series beginning in the mind--in this relation denominated _cause_--and developing into objective phenomena called _effects_ or an effect. The series being known by judgment we can infer similar causes from perception of similar effects. The commonest causation is the use and interpretation of language. Because we utter words from a certain motive we infer that all who utter the same words do so from the same motive. That is the reason of the intelligibility of words. This category is peculiar from the extremely narrow range of the experience which supplies the judgments. We never perceive any mind but one--our own--and this has to supply all the judgments by which we reason concerning other minds. There is therefore no category in which correct reasoning is so difficult and so rare. No amount of experience entirely overcomes this defect, for if we are ignorant we cannot understand the wise, and if we are wise we cannot conceive the motives of the ignorant and vicious. Only those persons who are mentally very like each other are mutually comprehensible. This category has a further peculiarity. In all the rest the inference relates to objective experience, and this being due to interaction of minds we are justified in saying that until it is perceived it has no existence. But in causation we are inferring something with reference to a mind, and this exists though we never can perceive it. We know that minds exist without perception because we know that our own exists though no one perceives us--though we are in total darkness and silence and cannot ourselves perceive our bodies. As already stated, Existence has not the same meaning when applied to objects and to minds, objects being merely temporary conditions of minds. The non-existence of inferred but unperceived objects does not follow from any defect in the faculty of inference, but depends on the essential character of objects. They are created by mutual contact of minds and cannot exist without that condition, however clearly they may be inferred and however correctly their appearance may be predicted.