Within Harry Potter, Harry is forced to confront what he fears the most time and time again. Harry fears Dementors that remove any happiness a person is feeling at the time and in Harry’s case forces him to relive particularly traumatic memories from his past. Thus when he is confronted with a boggart, a creature that takes the form of what you fear, it transforms into a Dementor itself. However, there are two different spells two combat the two different creatures, Riddikulis and Expecto Patronum. While the spells themselves combat different but similar creatures they seem to have a common force that must be used in order for either spell to have effect, some sort of happiness.
In the case of the boggart, a user must think of something particularly funny for the boggart to turn into when using the spell Riddikulis because laughter is what finished off a boggart. In one particular scene Neville, who is terrified of professor Snape, uses the spell and imagines Snape “wearing a long, lace-trimmed dress and a towering hat topped with a moth-eaten vulture and swinging a huge crimson handbag” (Rowling 137). While overtop compared to the remaining ways the students dealt with their boggarts it sends a picture, that something that makes you laugh or fills you with good natured thoughts can combat something we fear.
However, when Harry faces off against the Dementors he has to use a different spell, Expecto Patronum. The spell can only work if when stating the incantation the user is able to think of a particularly happy memory, enough so that either a shield or spirit form of the spell can act as a barrier and subdue the dementor. During the first few tries, when Harry is learning the spell with Lupin he is unable to conjure a sufficient shield form and is overwhelmed. However near the end of the novel, whereas previous times he was only able to conjure the shield, he was able to conjure “not a shapeless cloud of mist, but a blinding, dazzling, silver animal”, his true Patronus (411). Harry was able to succeed at that moment because he knew he had before, but the memory that had fueled him was the desire to see his father and to save himself and his godfather Sirius.
So when looking over and comparing the two spells side by side, it seems they both require the same similar emotion to work. Which is that Happiness or joy can combat fear, depression or darkness, both spells provide elements of light, Riddiculis, the psychical transformation of fear into funny and Expecto Patronum the psychical manifestation of light to combat the rippling dark of the Dementors. The spells seem to suggest that magic in the overall scheme is supposed to encourage joy and wonder and should be used in a positive light to make things better, not worse.