Association Psychology, as thus expounded, examines the links between experience as registered by a conscious mind and the ideas, or trains of ideas, which registered experience springs up. The strength or weakness of associations between a sensation and an idea or between ideas varies, depending on how permanent or vivid they are. Some associations are so firm and constant that they become indissoluble or inseparable, fusing the different aspects of the complex experience into a single cluster of associations. The vividness of a part of the cluster might engross the attention of the conscious mind. Sometimes the cluster is dominated by a sensation, sometimes by an idea. Generally speaking, Mill noted, sensations are more vivid than ideas, the painful or pleasurable sensations or ideas are more vivid than indifferent ones, and the more recent are more vivid than less recent ones (Mill 1829a, I.60–63). The perceiving mind attends only to a part of the sense experience, both at the moment of sensation and, consequently, in its copy, image or representation. In History of British India, Mill used this “law” of human nature to explain how a philosophic historian never had to set foot in a foreign country to write its history: