The words of a proposition are the signs of certain states of consciousness; and the thing alleged by a proposition is the connexion or disconnexion of the states of consciousness signified. When thinking is carried on with precision—when the mental states which we call words, are translated into the mental states they symbolize (which they very frequently are not)—thinking a proposition consists in the occurrence together in consciousness of the subject and predicate. “The bird was brown,” is a proposition which implies the union in thought of a particular attribute with a group of other attributes. When the inquirer compares various propositions thus rendered into states of consciousness, he finds that they differ very greatly in respect of the facility with which the states of consciousness are connected and disconnected. The mental state known as _brown_ may be united with those mental states which make up the figure known as _bird_, without appreciable effort, or may be separated from them without appreciable effort: the bird may easily be thought of as black, or green, or yellow. Contrariwise, such an assertion as “The ice was hot,” is one to which he finds much difficulty in making his mind respond. The elements of the proposition cannot be put together in thought without great resistance. Between those other states of consciousness which the word _ice_ connotes, and the state of consciousness named _cold_, there is an extremely strong cohesion—a cohesion measured by the resistance to be overcome in thinking of the ice as _hot_. Further, he finds that in many cases the states of consciousness grouped together cannot be separated at all. The idea of pressure cannot be disconnected from the idea of something occupying space. Motion cannot be thought {206} of without an object that moves being at the same time thought of. And then, besides these connexions in consciousness which remain absolute under all circumstances, there are others which remain absolute under special circumstances. Between the elements of those more vivid states of consciousness which the inquirer distinguishes as perceptions, he finds that there is a temporarily-indissoluble cohesion. Though when there arises in him that comparatively faint state of consciousness which he calls the idea of a book, he can easily think of the book as red, or brown, or green; yet when he has that much stronger consciousness which he calls seeing a book, he finds that so long as there continue certain accompanying states of consciousness which he calls the conditions to perception, those several states of consciousness which make up the perception cannot be disunited—he cannot think of the book as red, or green, or brown; but finds that, along with a certain figure, there absolutely coheres a certain colour.