From the intro:
"Illusionism has always been seen as a weaker form of magic, a school to be ridiculed rather than studied by most self-respecting mages. However, this book shall reveal that illusionism is neither to be scoffed at nor to be trifled with.
At its heart, illusionism is the art of deception, be it benign or malicious in nature. It alters another’s perceptions and tricks their senses. Those affected by illusions see, hear, smell, taste and feel things that are not there."