Cognition, knowing, and understanding are analysed in terms of levels, forms, and range. It is found that cognition is knowing and that understanding is a range of knowing. Three levels of knowing (pre-conventional, conventional, post-conventional), three levels of understanding (prehension, apprehension, comprehension), and six forms of knowing (linguistic, emotional, imaginal, physical, physiological, conative) are distinguished. Levels and forms of knowing operate as a system and constitute a range of knowing. One's range of knowing determines one's extent of understanding. The three levels and six forms of knowing are composed and contrasted with the categories of cognition posited by: Bloom, Engelhart, Furst, Hill, Krathwohl, and Masia; Bruner; Piaget; Gagne; Kohlberg; Collis and Biggs; and Maccia and Steiner. The conclusion is drawn that the three levels and six forms of knowing are critical, elemental categories and that the categories of knowing posited by other researchers are either subsets, combinations, or conflations of these elemental categories. (Author)