Detecting emotions can be considered to be the most difficult when it comes to sentiment analysis because all the emotions theories associated with detecting emotions. For example, a research paper by Paul Ekman and others believe that some emotions are more basic than others and emotions are associated with universal facial expressions and heart rate. However, not everyone agrees with this theory, which makes detecting emotions difficult. This result in different ongoing projects for detecting emotions, and all of these projects use different sets of data and different theories.