Researchers who want to study the concept and the emotion of courage have continued to come across a certain problem. While there are "numerous definitions of courage", they are unable to set "an operational definition of courage on which to base sound explicit theories". Rate et al. states that because of a lack of an operational definition, the advancement of research in courage is limited. So they conducted studies to try to find "a common structure of courage". Their goal from their research of implicit theories was to find "people's form and content on the idea of courage". Many researchers created studies on implicit theories by creating a questionnaire that would ask "What is courage?". In addition, in order to "develop a measurement scale of courage, ten experts in the field of psychology came together to define courage. They defined it as: