Magic in Pathfinder

Note: Much of this section was adapted from this article and also this article.

Types of magic
Magic in vanilla Pathfinder comes from a variety of sources. The exact nature of the fiction changes depending on the setting and who you're asking, but in general magic is either: Mechanically, the upshot is that the types of spells available to you is different depending on what kind of magic your class uses. Some classes and archetypes allow players to pick from multiple lists.
 * Arcane: A natural part of the universe that some people are able to tap into. These spells often require somatic components (complex movements) to cast, meaning that wearing armor inhibits their ability to cast spells. Arcane spellcasters are usually limited to wearing little or no armor, unless they take special feats, or their spells have a chance of failing. Arcane spells run the gamut from buffs to utility to damage to effects that are difficult to categorize.
 * Divine: Power granted from the gods to their favored servants. These spells are not subject to any sort of armor penalty, and so divine casters are able to throw as much heavy metal on themselves as they like. Divine spells are more limited in scope than arcane spells, but not dramatically. In general, there is more of a focus on buffs and utility and less on damage. Divine spellcasters typically are more adept at healing as well.
 * Psychic: Mental abilities that aren't truly magic, per se, but feel fairly magical. These are purely mental abilities, and so they don't have any sort of armor penalties.
 * Spell-like abilities: Some beings have access to abilities that ape spell effects, but aren't actually spells

Magic schools and domains
Most arcane spells fall into one of eight schools, with the exception of a few universal spells that do not belong to a specific school. Some classes or class options only allow spells from certain schools. Some schools have subschools, allows for further specialization.

Divine spells typically fall under a domain - which domains a given spellcaster has access to depends on their class and their chosen deity.

Some classes, including most pyschic casters, have systems unique to their class but which function similarly to the flavoring and limiting power of schools/domains.

Methods of Spellcasting
There are two forms of spellcasting in Pathfinder: Spontaneous and Prepared. Each has strengths and weaknesses, and dramatically changes the way a character uses magic in game.

Prepared Casting
Some spellcasters need to prepare their spells ahead of time in order to cast them later that day. The narrative justification is a bit hand-wavey (the spells are so complex that you can only memorize a few at a time, and you can't remember them for longer than a day) but the mechanical upshot is that a spellcaster of this type has access to a much greater list of spells than he will be able to prepare on a given day.

The strength of this class is that your spell list is often gigantic, allowing you a huge amount of customization and versatility. A wizard can fill almost any role in a party - damage, utility, healer, even front liner - if he prepares the right spells.

That, of course, is the weakness. Preparing the right spells in advance requires a bit of predictive guesswork. If your group finds themselves needing to infiltrate a retirement home, you're going to be hailed as a hero for having prepared Sands of Time. But what if you prepare it only to find yourself fighting clockwork soldiers which do not age? You'll be wishing you had prepared Disable Construct instead.

So, basically, prepared spellcasting puts limits on the number of spells a character can cast per day, and requires they prepare them ahead of time. In exchange, they can choose from a huge number of known spells to prepare each day.

Spontaneous Casting
Spontaneous casting will likely be more familiar to those who have played videogames with magic systems, or are familiar with books like the Harry Potter series. Spontaneous casters have innate magical ability, and cast spells intuitively, requiring no advance preparation. As long as they know a spell and have the energy to cast it, they're good to go.

The tradeoff is their list of available spells is much shorter. A sorcerer and a wizard might both be able to cast a fireball on Tuesday, but on Wednesday the wizard might opt for hurling lightning bolts, while the sorcerer is still only able to cast that fireball.

Spontaneous casters are typically able to cast a greater volume of spells in a given day or encounter, but their pool of options is small. Prepared casters cast a smaller number of spells, but can choose from a wide range of options as to what those spells will be.

Arcane Spellcasters: Divine Spellcasters: Psychic Spellcasters: ''*Arcanists are a bit of a unique case, as they are a wizard/sorcerer hybrid. In general, however, they must prepare their spells''
 * Prepared: Arcanist* (ACG), Magus (UM), Witch (OA), Wizard (CR)
 * Spontaneous: Bard (CR), Bloodrager (ACG), Skald (ACG), Sorcerer (CR), Summoner (PU)
 * Prepared: Cleric (CR), Druid (CR), Paladin (CR), Ranger (CR), Shaman (ACG), Warpriest (ACG)
 * Spontaneous: Hunter (ACG), Inquisitor (ACG), Oracle (OA)
 * Prepared: –
 * Spontaneous: Medium (OA), Mesmerist (OA), Occultist (OA), Psychic (OA), Spiritualist (OA)

CR: Core Rulebook

ACG: Advanced Class Guide

OA: Occult Adventures

UM: Ultimate Magic

PU: Pathfinder Unchained