If I have never heard a curlew, the cry which an unseen one makes, failsto produce an idea of the bird. And on remembering what various trains ofthought are aroused by the same sight, we see that the occurrence of eachfaint manifestation chiefly depends on its relations to other faint manifestationsthat have gone before or co-exist.

Here we are introduced, lastly, to one of the most important of the differencesbetween those two orders of manifestations. The conditions of occurrenceare not distinguished solely by the fact that each set, when identifiable,belongs to its own order of manifestations. They are further distinguishedin a very significant way. Manifestations of the faint order have traceableantecedents; can be made to occur by establishing their conditions of occurrence;and can be suppressed by establishing other conditions. But manifestationsof the vivid order continually occur without previous presentation of theirantecedents; and in many cases they persist or cease in such ways as to showthat their antecedents are beyond control. The sensation known as a flashof lightning, breaks across the current of our thoughts absolutely withoutnotice. The sounds from a band that strikes up in the street or from a crashof china in the next room, are not connected with any previously-presentmanifestations, either of the faint order or of the vivid order. Often thesevivid manifestations, arising unexpectedly, persist in thrusting themselvesacross the current of the faint ones; which not only cannot directly affectthem, but cannot even indirectly affect them. A wound produced by a blowfrom behind, is a vivid manifestation the conditions of occurrence of whichwere neither among the faint nor among the vivid; and the conditions to thepersistence of which are bound up with the vivid manifestations in some unmanifestedway. So that whereas in the faint order, the conditions of occurrence arealways among the pre-existing or co-existing manifestations; in the vividorder, the conditions of occurrence are often neither present nor can bemade present.

Let me briefly enumerate these distinctive characters. Manifestationsof the one order are vivid and those of the other are faint. Those of theone order are originals, while those of the other are copies. The first formwith one another a heterogeneous current that is never broken; and the secondalso form with one another a heterogeneous current that is never broken: or, to speak strictly, no breakage of either is ever directly known. Thoseof the first order cohere with one another, not only longitudinally but alsotransversely; as also do those of the second order with one another. Betweenmanifestations of the first order the cohesions, both longitudinal and transverse,are indissoluble by any direct action of the second order; but between manifestationsof the second order, these cohesions are most of them dissoluble with ease.

While the members of each current are so coherent with one another that itcannot be broken, the two currents, running side by side, have but littlecoherence. The conditions under which manifestations of either order occur,themselves belong to that order; but whereas in the faint order the conditionsare always present, in the vivid order they are often not present, but liesomewhere outside of the series. Seven separate characters, then, mark offthese two orders of manifestations from one another. §44. What is the meaning of this? The foregoing analysis was commencedin the belief that the proposition postulated by Philosophy, must affirmsome ultimate classes of likenesses and unlikenesses, in which all otherclasses merge; and here we have found that all manifestations of the Unknowableare divisible into two such classes. What is the division equivalent to?