 In some circumstances, a person may form a reasonable belief that the exciting cause of the appearance of a certain sensation at one time is a certain object perceived by sense at a proximate time. The “exciting” cause is the component of the entire cause which is present just at the moment the effect occurs and absent whenever it does not occur; other requisites of the cause are relatively permanent conditions which may be known or unknown. A belief that such-and-such an object is the exciting cause of such-and-such effect arises from perception of similarities and differences among successive sensations. This may prompt another implicit rudimentary argument: this sensation has a cause; the cause is some entity (perhaps consisting of several objects) that was not present before the sensation appeared and was present at the moment it appeared; there is one and only one thing of which this is true; so it is the exciting cause of the sensation. Her example is finding that a view is present in consciousness when you open your eyes and absent when you close them. Because the position of the eyelids is the one and only candidate to be the exciting cause, you are likely to believe it is the active cause. Shepherd is well aware that such a belief might be mistaken. Still, she maintains that we form many beliefs in this simple way, and a great many of them turn out to be true. More exacting purposes demand beliefs that are formed with more care (see  5.1), but the basic reasoning is the same. 