But since when one thing has been set in motion another thing may be moved by it, and imagination is held to be a movement and to be impossible without sensation, ie to occur in beings that are percipient and to have for its content what can be perceived, and since movement may be produced by actual sensation and that movement is necessarily similar in character to the sensation itself, this movement cannot exist apart from sensation or in creatures that do not perceive, and its possessor does and undergoes many things in virtue of it, and it is true and false.