The essay "The Nature of Theory in Information Systems" by Shirley Gregor explores the structural nature of theory within the Information Systems (IS) discipline. Despite the importance of theory, questions about its form and structure are often neglected. The essay addresses issues of causality, explanation, prediction, and generalization, which are fundamental to understanding theory. It proposes a taxonomy that classifies IS theories based on how they address four central goals: analysis, explanation, prediction, and prescription. Five types of theories are distinguished: (1) theory for analyzing, (2) theory for explaining, (3) theory for predicting, (4) theory for explaining and predicting, and (5) theory for design and action. The essay provides examples to illustrate each theory type and demonstrates the applicability of the taxonomy by classifying a sample of journal articles. It contributes by showing that multiple views of theory exist and by exposing the assumptions underlying different viewpoints. The essay also suggests that the type of theory being developed can influence the choice of epistemological approach. The paper advocates for the legitimacy and value of each theory type and encourages the development of integrated bodies of theory that encompass all types.The essay "The Nature of Theory in Information Systems" by Shirley Gregor explores the structural nature of theory within the Information Systems (IS) discipline. Despite the importance of theory, questions about its form and structure are often neglected. The essay addresses issues of causality, explanation, prediction, and generalization, which are fundamental to understanding theory. It proposes a taxonomy that classifies IS theories based on how they address four central goals: analysis, explanation, prediction, and prescription. Five types of theories are distinguished: (1) theory for analyzing, (2) theory for explaining, (3) theory for predicting, (4) theory for explaining and predicting, and (5) theory for design and action. The essay provides examples to illustrate each theory type and demonstrates the applicability of the taxonomy by classifying a sample of journal articles. It contributes by showing that multiple views of theory exist and by exposing the assumptions underlying different viewpoints. The essay also suggests that the type of theory being developed can influence the choice of epistemological approach. The paper advocates for the legitimacy and value of each theory type and encourages the development of integrated bodies of theory that encompass all types.