So, you're interested in Patronuses, and would maybe even like to conjure a Patronus yourself? Well, you've come to the right place! I will do my best to share my knowledge of this fascinating subject. Before we begin, however, let me warn you, the Patronus Charm is a very difficult skill to master, and should you be successful, the animal which appears from the tip of your wand may not be the creature you'd expect at all! Even so, this is a very interesting subject, and there's lots to learn, so let's jump right in, shall we?

What exactly is a Patronus? The word “Patronus” comes from  Latin and basically means a “patron” or “guardian.” In ancient Rome, a patron was a rich, powerful male who would defend those who were his clients against lawsuits, help them find jobs, and pay them a fee for the services they completed for him. The client would appear at the patron's home each morning to see if there were any errands which needed to be completed. This patronage was how young, wealthy Roman males moved up the social ladder and gained power. In the wizarding world, perhaps the best example is Cornelius Fudge's guidance of Percy Weasley.  And there have, of course, been several female patrons of note throughout history, including Ancient Egypt's Queen Hapshepsut, Catherine de' Medici, Queen of France, and England's Queen Elizabeth 1. 

According to this excellent definition by Cattulus Spangle, a Charms researcher who lived during the 18th century, taken from his book Defence and Deterrence: “The Patronus is the awakened secret self that lies dormant until needed, but must now be brought to light.” This definition gives us several clues about our subject. If we break it down into small parts, it seems to be saying that there is a part of each of us that is hidden and unknown, either by ourselves and/or by others, and that this part is currently asleep. Some event happens where we need that hidden part of ourselves, so we must find it, awaken it, and make it known. The Patronus is the visible form we actually bring forth to represent our hidden selves, and because the word “light” is used, that tells us its form appears as a light, and isn't dark at all..

According to The Standard Book of Spells, author Miranda Goshawk tells us that the Patronus is our strongest positive feelings, which take the form of a guardian animal, with the animal being one that we have a deep affinity for. She also tells us that, while we may think we know the animal form of our Patronus, we can never be completely certain until we actually conjure our Patronus. Our animal form may even be a part of ourselves that we lack but deeply desire, such as a family, freedom, or a more playful attitude. 

Remus Lupin explained to Harry Potter that the Patronus is a positive force. "The projection that the Dementor feeds upon - hope, happiness, the desire to survive" is not a part of it. Unlike humans, the Patronus cannot feel sadness or despair, only positivity.  

What is the purpose of a Patronus? As Remus Lupin stated above, the Patronus Charm can be very effective against Dementors. A Dementor is a dark, evil creature which lacks a soul. It creates an atmosphere of misery and despair so profound that muggles, who cannot see Dementors, directly feel their effects. Dementors feed on happiness, which is the very opposite of what they themselves do not possess, and this results in leaving any person in close proximity to a Dementor with dark feelings of depression and despair. The Patronus attracts the Dementor, but the creature cannot harm it, because the Patronus contains only positive emotions and protects the person who casts the charm. The intense feelings of happiness overwhelms and eliminates the sadness and despair. This is why the Patronus is considered to be the most powerful protector of humans against Dementors. 

Thanks to Flavius Belby, we have also learned that the Patronus Charm will also protect you against a lethifold attack. This charm saved his life from one of their attacks, and he is the only known survivor of a lethifold! What's a lethifold, you ask? It's a creature which looks like a black cloak. It attacks while the person is sleeping, suffocating and then consuming them. 

Albus Dumbledore created a third use for the Patronus Charm. He needed a method for the members of the Order of the Phoenix to communicate, which would be secure from dark arts tampering. The Patronus cannot be faked or impersonated, because it is such an intregal part of who the person is, and each Patronus is unique according to the witch or wizard who casts it. A Patronus can deliver messages and it speaks using the voice of the person who cast the Patronus. A good example is when Minerva McGonagall cast three Patronuses to ask for help from the other Heads of Houses when Harry Potter came back to Hogwarts.

A Patronus can take one of two forms: corporeal or non-corporeal. A Corporeal Patronus takes the form of a fully formed, identifiable animal. The animal is bright silver and translucent. It is the strongest of the two forms, and can drive away Dementors. A Non-Corporeal Patronus is often described as a thin, silvery mist which does not take any particularly well-defined form. While not especially effective at driving away Dementors, it is an effective shield against them, and is the preferred form of Remus Lupin, who chose to hide his wolf Patronus, perhaps because it reminded him of his werewolf condition. 

By the way, while we're on the subject, a Patronus and an Animagus are not the same. An animagus is that rare witch or wizard who has the ability to transform themselves into an animal. We know that Minerva McGonagall's Animagus form and her Patronus form were both tabby cats, and James Potter's were both stags, so it appears the two shapes may influence each other, but there's still much to learn about Animagus forums. Do the two forms always match? Does the Animagus form ever change, or does it remain the same? We will discuss the Patronus and the circumstances in which it's form can change in a future lesson.

There may also be some confusion about Patronuses, Spirit Animals, Totem Animals, and Familiars. 

A Spirit Animal, rather than coming from you, will appear to you, in order to teach you some lesson you need to learn. Just like a Patronus, you do not choose the animal, and they are not there to guide you. 

A Totem Animal is an animal that you feel connected to and that you can call upon to guide you when you are going through difficulties. A totem can represent an individual as well as a large group of people. It differs from a Patronus in that, while you may not feel connected to your Patronus because it represents who you truly are at your core or what you deeply lack, your totem is an animal you yourself would choose to influence your behavior. 

A Familiar is a spiritual entity which helps with communication between the human, animal, and spiritual worlds.