Intellectual assessment tasks vary both in the degree and nature of complexity of the problem-solving situation. In order to provide a precise language for describing problem solving, the language of classical decision theory is used to describe intellectual assessment tasks. The ‘structuredness’ of a problem is defined as a lack of specificity of certain parameters of decision theory. The language of inquiring systems is employed to describe differences in the conditions under which a problem can be considered solved. Differences in inquiring systems are outlined along the dimensions of the decision theory and structure terminology defined above. Formal operations and other well-structured problem-solving skills are compared to post-adolescent cognitive development, which deals with the ability to solve ill-structured problems. Distinctions are made between various types of ill-structured problems. Implications for problem-solving performance are discussed.