Economics is the most prestigious and best-paid, social science. The scientific method of economics is largely theoretical: "Models make economics a science" in the words of a respected contemporary economist. The distinction between two kinds of explanation, causal and outcome-based, is essential to a proper understanding of economics, where outcome-based theory dominates. By the end of the 18th century, technological advance had become a major, possibly the largest, force for economic change. There are several strategies, each flawed in its own way such as commonsense verbal description, more or less sophisticated mathematization, the individualistic, nonmathematical, axiomatic approach of the Austrian School and, behavioral economics. Behavioral economics uses experiments with human and animal subjects in contrived situations as a way to unpack the concept of rationality. Economics is perhaps best thought of as a set of questions generated through some form of optimality analysis: as pertinent questions, rather than quantitively defined answers.