It may seem strange that the verb which signifies existence should have been employed in so many different languages as the sign of predication, if there is no real connection between the two meanings. But languages have been built up by the extension of an originally small number of words, with or without alterations of form, to express new meanings, the choice of the word being often determined by very distant analogies. In the present case, the analogy is not distant. All our predications are intended to declare the manner in which something affects, or would affect, ourselves or others. Our idea of existence is simply the idea of something which affects or would affect us somehow, without distinction of mode. Everything, therefore, which we can have occasion to assert of an existing thing, may be looked upon as a particular mode of its existence. Since snow is white, and since snow exists, it may be said to exist white; and if a sign was wanted by which to predicate white of snow, the word exists would be very likely to present itself. But most of our predications do relate to existing things: and this being so, it is in the ordinary course of the human mind that the same sign should be adhered to when we are predicating something of a merely imaginary thing (an abstraction, for instance) and that, being so used, it should create an association between the abstraction and the notion of real existence.--_Ed._]
{ 179} We have now observed, wherein Predication consists, and the instruments by which it is performed. { 180} We have also, in part, contemplated the End which it is destined to fulfil; that is, to mark the order in which sensations and ideas follow one another in a { 181} train. On this last part of the subject, however, the following observations are still required.
The trains, the order of which we have occasion to { 182} mark, may for the elucidation of the present subject, be divided into two classes. We have occasion to { 183} mark, either, first, The series of the objects we have seen, heard, or otherwise perceived by our senses; or, { 184} secondly, A train of thoughts which may have passed in our minds.
1. When we come to record a train of the objects we have perceived, that is, a train of sensations, the sensations have become ideas; for the objects are not now acting on our senses, and the sensations are at an end.