Features are the individual properties of a knowledge component that determine the retrieval conditions of that knowledge component. Sometimesfeatures are relatively directly perceivable (seen or heard). In the language literature, such features are called cues (ref?). Sometimes the relevant features of a knowledge component require more complex inference to be detected by the student. For example, Chi, Feltovich, and Glaser distinguish between shallow features of physics problems, like pulley system or inclined plane, that are irrelevant to correct problem solving (i.e., KC application) and deep features, like conservation of energy, that are relevant to accessing correct knowledge components.