Expertise: perception and similarity, memory and categorization, problem solving. Look at 3 studies (look at parts highlighted in lecture) Aren"t just smart : although in many cases might also be very smart intelligence in of itself is not what we are talking about. At least 10 years of study/practice (ericcson) Show differences in novices in ability to categorize and memorize, judgements about topics and objects and solve problems in a way that"s fundamentally different than novices. Expert knows how to solve new problems: has set of skills for solving new problems, for ill formed problems, expert can find operators that apply to new problems. Simply knows the answer to many similar problems: has lots of prior experience, need not start from scratch solving problems, bc solved similar problems in past; remember details of similar problems. System 2: slower, rule based, reasoning, evolutionarily more recent.