Empathy refers to the projection of oneself into the personality of another in order to achieve better understanding.
Sympathy describes an affinity of feelings between people.
Compathy refers to feeling with another person.
Compathy differs from sympathy in that compathy strictly refers to one’s feelings (happiness, sadness, joy, sorrow), whereas sympathy can also refer to political opinions, intellectual ideas, and even physiological relations.
In other words, one person's emotional presentation triggers a tangible response in an observer.