Taxanomy is the science of classification, by naming, describing, and classifying. Using taxonomy, Benjamin Bloom has categorized intellectual behavior into three overlapping realms - the cognitive, psychomotor, and affective. The cognitive realm has 6-levels: knowledge, comprehension, application, analysis, synthesis, and evaluation. These were later revised. It is widely used by educators to set objectives of lessons and formulating questions that motivate thinking appropriate to each level of the hierarchical pyramid.