Editing Ars Magica (section)

===Magic system===
The centerpiece of ''Ars Magica'' is the system of Hermetic Magic devised by Bonisagus.  It consists of 15 '''Arts''', divided into 5 '''Techniques''' and 10 '''Forms'''.  This is sometimes called a "Verb/Noun" system: the Technique is the verb (what effect the magic has), and the Form is the noun (the entity, object or substance that is affected or brought forth).  These 'verb-noun' combinations can be used to cast both '''Formulaic''' spells (which are recorded in texts, are learned through study and mastered through experience, and have known, fixed effects) and '''Spontaneous''' spells (which a caster improvises with no prior knowledge other than the Arts themselves, giving the potential results greater flexibility but lower potency).  Every apprentice (with a few [[Order of Hermes (Ars Magica)#Houses|Ex Miscellanea]] exceptions) is "opened" in all 15 Arts before fully joining the Order; each Art begins with a Score of 0 and a mage may usually only increase one of them during a season (see below).

Each Technique is named by a first-person singular present tense [[grammatical mood|indicative]] Latin verb:
*'''Creo''' ("''I create''") brings objects and substances into existence from nothing, or makes an already-existing target a "more perfect" version of itself (e.g. healing magic, as healed bodies are nearer perfection than wounded bodies).
*'''Intellego''' ("''I perceive''") detects or reveals, enhances a target's natural [[sense]]s or conveys supernatural ones.
*'''Muto''' ("''I transform''") alters the nature of a being, object or substance, adding unnatural traits and/or removing natural ones.
*'''Perdo''' ("''I destroy''") decays, disintegrates or otherwise diminishes the target, making something a worse example of its kind (i.e. the opposite of ''Creo'').
*'''Rego''' ("''I control''") involves manipulation of the target in any way that does not alter its nature, e.g. direct a target's movement, put a creature to sleep, or force a tree to bear fruit out of season.  This is the main Technique used in spells of protection or 'warding'.

Each Form is named by a singular [[Accusative case|accusative]] Latin noun:
*'''Animal''' affects "all natural living things that are not plants or humans, doing to animals what ''Mentem'' and ''Corpus'' spells do to people" as well as "things made with animal products" such as leather, wool, cheese, silk, etc.  Since [[bacteria]] were unknown in medieval times, illness (e.g.) was considered either a form of [[Demonic possession|possession]] or an imbalance of '[[Humorism|bodily humors]]'; thus, magic dealing with disease is relegated variously to ''Creo'', ''Mentem'' and/or ''Vim'' effects.
*'''Auram''' affects lightning, wind and gaseous substances; other weather effects typically require an ''Aquam'' requisite (see below).
*'''Aquam''' is used for any liquid, with the exception of blood (which requires ''Animal'' or ''Corpus'' magic to affect); non-liquid forms of water will involve requisites (see below).
*'''Corpus''' (the incorrect declension ''Corporem'' was used in older editions) applies to the human body, making it crucial to longevity formulas.
*'''Herbam''' primarily involves plants, but applies equally to any organic matter, living or dead, that is not of animal origin.
*'''Ignem''' involves light and heat, and is heavily represented in the fire spells of House Flambeau.
*'''Imaginem''' (previously ''Imagonem'') deals with images, sounds, and other sensory stimuli (thus is involved in most illusionary effects).
*'''Mentem''' deals with emotions, memories, thoughts and spirits.
*'''Terram''' involves earth and minerals: mere soil is the simplest target, while stone, metal and gems require progressively greater investment of spell levels to achieve the same effect.
*'''Vim''' ("power") involves magic itself, as well as demons (the overlap is not widely understood, but the fact that there is one is a significant obstacle to the Order's 'public relations', particularly concerning the [[Christian views on magic|Church]]).

A mage's skill when casting a spell is the sum of their scores in the appropriate technique and form.

Some spells involve more than one Technique, and/or more than one Form at once; each Art used in addition to the basic pair is called a ''requisite''.  All relevant Art Scores are compared: the caster's lowest Technique and lowest Form are used, reflecting the limiting of the caster's magical knowledge.

Regardless of how high one's Art Scores may rise, there are outer boundaries to the application of Hermetic Magic (whether Formulaic, Spontaneous or even Ritual).  Bonisagus's theory outlines a set of inherent '''Limits''', similar in concept to the [[Physical law|laws of physics]]; the two central, 'Greater' Limits are:
# Magic cannot influence a pure manifestation of the Divine; while earthly Relics (however sacred) and agents of the Divine (anything "separate from the mind of God") may be resistant to magic they are not immune, but it is impossible to (e.g.) interfere with a Miracle (which may be prayed for by an agent or supplicant, but is itself a direct intervention by Divine will).
# Magic cannot permanently change a target's [[Nature (philosophy)|Essential Nature]] (the implications of which vary depending on the target in question).
There are also eleven 'Lesser Limits' (addressing more specific 'blind spots' such as aging, creation, time and the [[soul]]) which are generally thought either to derive from the two Greater Limits, or to be flaws in Hermetic Theory which may eventually be 'corrected'.

Additional statistics for every spell (which have been redefined in nearly every new edition of the game) are Target (what or whom the spell is directed at), Range (how far the Target may be from the caster), and Duration.
For reasons of [[Balance (game design)|balance]], some spells require the expenditure of "vis" – magical essence in physical form – which all magi and covenants tend to make a point of hoarding and/or trading.  No ''Creo'' effect, for example, can be permanent unless vis is consumed during the casting.
Some Formulaic Magic is so effective that it can ''only'' be achieved with vis and an elaborate, time-consuming ritual (hence, '''Ritual Spells''').  This automatically applies to any spell of a greater Level than 50, any spell with a Duration of 'Year', and any non-Imaginem spell with a range of 'Sight'.