Magic

Magic (魔術) is a term used to refer to supernatural phenomena that cannot be explained or analyzed via any sort of scientific means and reasoning. In the Toaru Majutsu no Index universe, magic is a complex system of arts, disciplines, and traditions that are firmly grounded in laws and knowledge that are wholly unknown and beyond the grasp of human sciences, which sought to manipulate and distort certain aspects of reality.

Also called the occult, conflicts with the magic side, the secret underworld that deals with magic and the occult, are the primary and most recurring plot points of the series.

History
Magic by itself roots from the simple fact that 'those without talent' wanted to be able to do the same things as 'those with talent' - namely Esper and Gemstones.

Principles
In contrast to espers who have only one ability that is decided by birth, magicians can create many supernatural phenomena without restrictions, but they have to take the time and effort. Additionally, all forms of magic are based around a certain ideological premise. This kind of premise can originate from almost anything culturally narrative including religions, belief systems, mythologies, or even folklore and fairy tails.

It should be noted that it is possible to derive magical powers from no particular source but such a method is far too inefficient and complicated for practical purposes. The magician would have to create an entire system of rules and commands from the ground up

Energy
The overall concept of magical energy is largely controversial to even magicians themselves. Different denominations and schools of thought have their own theories on the idea of how magical energy precisely works in conjunction with a human's life force, namely the soul. Leivinia Birdway has compared the soul to that of crude oil and therefore must be properly refined into usable magic.

Mana
Mana is the energy that allows magicians to use magic. Mana exists in all forms of life, not just magicians, although they are the only ones who use it. It has been explicitly stated one method of creating mana is by processing a person's inner life force. The various schools of magic, for example Nordic and Shinto styles, requires different 'kinds' of mana for casting that other styles might not use.

There is 'natural' mana that exists within the earth itself, which some magicians or magical objects, such as the grimoires, draw their power from, in the form of "leylines". Mana is incompatible with the AIM fields that espers produce, as a result, whenever an esper performs magic he/she becomes severely injured. This incompatibility largely results from a combination of the human body's inability to host two different power systems at the same time and the different methodology imposed.

Mana can be "inserted" into objects following complicated rituals, which can give birth to "magical items" that posses magical properties on their own, for example in one opportunity Index references the ritual needed to add power to a holy cross.

Experts theorize that since Mana comes from the caster's life force, then immortal beings would possess an infinite amount of Mana, having access to unlimited and powerful magic that no magician would be able to fight against. This is one reason why Vampires are thought to be invincible by various people on the Magic Side.

Ley lines
A ley line is a current of power that runs through the earth, using a number alignments using terrain and monuments, among other geographical interests. Ley lines are alterable by destroying and altering the terrain that runs through it, or applying the art of feng shui. However, modification of ley lines is a delicate process, as making a mistake can cause disastrous results. As such, modifications of ley lines are often carried out as big national projects and magicians who use earth for their magic are forced to be careful lest they destroy important magical points.

With modifications, ley lines can be used to strengthening the power that flows through a ley line, or as something akin to pipelines. Ley lines can be described as pipelines and the nodes where they meet up for example, the Avignon and the Vatican, act as reservoirs where other pipes are connected. With this, certain affects can be achieved, such as a spell travelling through the ley line from a node to another node, which will then spread that spell's effect through the ley lines it is connected to.

Instruments and tools
Any well-practiced magician can easily perform magic simply by channeling magical energy through their bodies but it is often more convenient to enhance or focus that energy through the use of various tools and instruments. These items are known as "spiritual tools". The physical nature of the tool itself is irrelevant as only the shape and function needs to be preserved. Thus, a simple umbrella can easily proxy as a spear and the closer the object is to its intended purpose, the more effective a spell is and the chance of failure decreases. However, here is also a limit to this replication acceptance. Certain powerful powerful and holy artifacts simply cannot be copied at all in order to yield the desired effect such as the Spear of Longinus or Joseph's Holy Grail due to the discrepancy in power level.

A spiritual tool, in its design, is an object that is intended to further refine the magical power within a human and thus they are in a way, an extension of a magician's body. Caution must be taken so that when a spiritual item is destroyed after its usefulness has passed, the magician does not sever a part of his or her life force along with it.

Idol Theory
Idol theory is the underlying explanation to how magic works, much like how personal reality explains the roots of esper abilities. This phenomenon refers to an imitation of a whole or parts of a subject, the source, gains properties and attributes that are inherent to that source. Basically, objects or events contain certain symbolic meanings and powers and thus it is possible to draw on that power by imitating, altering, or magnifying said object or event. A simple cross placed in a church can duplicate the Cross that the Son of God was crucified on, and accordingly will duplicate its holy power.

Under Idol Theory, the inverse can also occur. Changes upon an idol will also affect the original source.

Styles
Many of the magic spells etc. is based on a certain set of laws - e.g. Celtic or Norse. But there are no strict division, because one base can be based on another base - e.g. Norse mythology was influenced by Celtic culture. However, magic users often use magic that is inherently part of their culture, like Kaori using her Amakusa spells based from Shinto, Buddhist, and Christian origins.

In the end, religion tends to plays a key role in magic, as cultures and traditions of a certain population are tied to it. For example, Agnese Sanctis once believed that all magic that does not stem from Roman Catholicism is black magic.

Western magic
As the West is dominated by Christianity, most magic users are influenced by it one way or another, alongside whatever cultural traditions they've grown up with. This also includes pagan or pre-Christian origins, for example the Roman Catholics, despite their stringent adherence to the use of their own magical traditions, used Wooden Stake magic, the origins of which came from the Pythagorean Order. As well as the magic names used by English magicians used Latin

Difference with esper abilities
The difference between espers and magicians is that an esper have normally only one ability, while magicians can create many supernatural phenomenon. But magicians have to take effort and time, while esper can use it anytime. The other thing is that the abilities of the espers depends on the environment - e.g. an esper who produce fire can't produce it without oxygen - while magicians don't have this restriction.

Magic names
As stated before, magic exists to fulfill a wish for the user. Accordingly, all magicians possess a magic name in order to set up a goal that they wish to set their desires around summed up as a Latin word (i.e. Fortis, Honos, Regnum, etc.). A magician will dedicate the rest of his or her life by whatever means to achieve those goals that have been carved into his or her soul. A magic name then concludes with a three digit number so as to avoid identical names and is accompanied by a phrase often as a description of who they are and an elaboration of their disposition.

Magic names can also serve a second purpose. Due to tradition, magicians are never supposed divulge their real names. In practice, magic names are used instead and they are only declared to other people as an official declaration of malevolent intent.

Organizations
Magicians often use an organization like magic cabals or denominations to realize their goal found within their magic names.