Sections 17.2.1 and 17.2.2 give two reasons for using formal methods in HCI: communication and analysis. These are focused on the sort of mathematical models found in this chapter. However, there are other sorts of ‘formal’ modeling in HCI: dialog notations are formal models of the syntax of the human–computer conversation, hierarchical task analysis is a formalization of the task structure, some cognitive models are effectively formal models of the user’s mind. a. Are communication and analysis reasons for using these other sorts of formalism? b. Can you think of other reasons why you would or would not use formalisms? c. Try to use these pros and cons to formulate issues in the choice of appropriate forms of formal model and analysis.