Magic is the science you don't know yet. The science you already know is engineering. -- RecklessPrudence
The nature of magic is one of constant debate. Any sufficiently advanced technology can be indistinguishable from magic. Any sufficiently analysed magic can be treated like science. But, overall, anything that can not fit into the rules of science can be called magic.
Conjuring is always a good one. Making things, even temporarily, from thin air defies the laws of thermodynamics. Levitation defies the laws of physics. Science can take the molecules of a sow's ear and transform it through laborious processes into a silk purse, but magic can do it in seconds with a simple transmogrification spell.
Which has lead, more or less, to the Magical Investigation Society.
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