We all know what magic is- even if you happen to have not been taught about it in school, which you should've been, there's no creature on this planet, and especially no pony, that doesn't know what magic is, especially considering to the extent of which it is used by, obviously, unicorns, but both earth ponies and pegasi as well- either way, the last earth pony, pegasus, or unicorn-only villages have been discovered and introduced the wider world already, so there isn't any way that ponies haven't encountered the most, for lack of a better word, flamboyant magic user, that being the unicorn.
However, even a few unicorns don't understand the extent to which magic can vary. They use spells, they learn basic or even slightly advanced magical theory, but often don't care enough to continue classes in magic, often resulting in only a basic or, again, slightly above basic understanding of magic. Spells, however, branch into multiple different 'types' of magic; that being said, there really aren't separate magics, but different ways to utilise magic. This is turned into the branches I earlier mentioned.
This chapter is going to be entirely about those branches- now, before you understand branches, you must understand that they all spring off of the main 'type'- ether magic. This is what every branch of magic, in some sense, embodies- from light to dark, from harmonic to chaotic, from technological to fantastical, every branch is directly related to ether magic. Now, branches of magic are rather simply described- first we have light magic, the most commonly used magic and in fact, most ponies rarely, if ever, learn spells not in the light or occasionally white branches of magic.
Light magic can be described by talking of spells that feed on low-level positive emotions, such as joy or anticipation. Basic telekinesis, which takes the strength of a unicorn and funnels it through the air to 'grab' an object, is powered entirely by happiness. White magic can be described by talking of spells that feed on high-level positive emotions, such as love or nostalgia.
Then, the infamous dark magic- fed by low-level negative emotions, such as nervousness or sadness. Black magic, however, is often confused with dark magic- this is not a mistake that should ever be made. A pony making use of dark magic is not evil, or misguided, or anything of the sort- dark and light are both fine to use, and should in fact be used together to achieve maximum efficiency. In fact, a lot of ponies have nearly definitely accidentally powered spells via dark magic, since telekinesis- for example- can easily be powered by either.
Anyway, black magic is powered by high-level negative emotions, such as rage or loss. Now, overuse of a certain magic can lead to an 'infection' of emotion, which is why ponies are generally happy creatures, though not caring much about procreation; we are practically powered by light magic. This isn't a good thing, and is actually a slight problem- we are too happy, and our over-reliance on light magic should be fixed.
Both black magic and white magic, however, are not recommended. High-level emotions 'infect' you both easier and faster, as the spells powered by them are always, with no exception, more powerful- a one-time use of black or white magic to lift a boulder off of a pony, or to perform incredible feats in general, is fine, but even twice in a day can lead to too much of whatever emotion is being used. Before saying anything, too much love is bad because you basically become, pardon my language, a sexual machine stopping at nothing to forcefully... well, yeah.
Nostalgia will put you into a coma unless you have a high mental resistance or magical tolerance, rage will make you incredibly violent, and loss will sink you into a suicidal state that only more high-level spells can break you out of. Of course, there are other high-level emotions- lust, hate, etcetera, but these are the most commonly used. Sombra, for example, was powered by black magic- a mix of anger and loss mingled in his brain overwhelmingly after he was analysed post-mortem. Dinky Doo, the rapist of nearly a thousand? A one-time use of white magic to save her mother when she was a filly and therefore with a low level of mental and magical resilience transformed her.
Needless to say, the other branches are so much harder to access. Most ponies don't access harmonic magic since you must strike a balance inside yourself- an interesting magical concept covered in a later chapter- to use it. Chaotic magic is incredibly specialised, and is comprised nearly entirely of reality-warping spells; a pony must be magically diseased while striking a balance to use it, and these spells put a massive strain on the horniglymphene, modes, and can empty a mana pool in seconds.
All other branches branch off of light, dark, black, white, chaotic, and harmonic. There are also natural magics- these are such as the alternate magic, which lets a pony talk to the dead, spirits, temporarily at their order. Ponies with this are either caught and taught to use it early or they degrade into a rambling mess due to information overload. Stellar magic is fairly self-explanatory, and known to be wielded only by Princess Celestia and Princess Luna in recorded history, though multiple myths unconfirmed by the sisters circle that Discord, Cadance, and other demi-godly creatures can access it.
As of now, no other magics have been turned into branches directly sprouting off of ether, though there's a large possibility that one day a pony will enter a certain state or use a certain thing and a new branch will be discovered- harmonic magic, for example, was my discovery after weeks of studying the Tree of Harmony and all notes we had of the Elements of Harmony.
Before I end this chapter, let me quickly clear something up: pegasi and earth ponies do not use any branch of magic to fuel their own naturally-occurring abilities- when utilising unicorn-style spells actively they do, but otherwise their abilities are left without influence from emotion. They are, however, still joyful simply due to exposure to mass amounts of light magic casting. Now put the book down and stop for a tea break or something- I know not everyone likes to read as much as me!
Though, I certainly wouldn't argue if you continued!