Direction on the construction and application of classification schemes such as taxonomies is readily available, but relatively little has been offered on evaluating the schemes themselves and their use to categorize content. A classification scheme can be judged for how well it meets its purpose and complies with standards, and a strong evaluative framework is reflected in S.R. Ranganathan's principles of classification. The degree of certainty of classification decisions depends on objective understanding of the object to be classified, the scope and details of the class and the coverage and organization of the overall classification scheme. The more complete the information about each class, the more reliable the goodness- of-fit for an object to a class is likely to be, whether chosen by human or machine classifiers. This information comes through definitions, examples, prior use and semantic relationships. The risk of misclassification can be reduced by analyzing the goodness-of-fit of objects to classes and the patterns of missed or erroneous selections.