What is Mentalism to you?
To me, mentalism is the branch of magic that
appears to use no props or gimmicks, relying entirely on the magician's apparent mental prowess.
You can, of course, use sleight of hand or a prepared prop or a gimmick to accomplish the effect. The important part is that your presentation inherently relies on an audience perception that you didn't use them. There are all kinds of mentalism effects which actually do use rather elaborate setups and props and gimmicks, but the audience is misdirected into the belief that these are not part of the trick.
Take, for example, the old card index. You write a prediction on a piece of paper, and stick it in your pocket; you allow the spectator to fairly mix and shuffle the deck before selecting a card; and meanwhile, you have
all the cards written down on little slips of paper in your pocket, so you simply locate and produce the correct slip. This is clearly a gimmick, and the deck of cards is clearly a prop, but you would normally present it as though neither is necessary - because you are reading the spectator's mind.
Most tricks can be presented as mentalism. A simple card force can turn into mentalism: "I'm getting a black card... it's not a face card... it's a high value... an even value... and I'm getting an impression of sharpness... the eight of spades?" What matters isn't the trick itself, but the way you present it, so I sort of roll my eyes at the idea of mentalism being a category of magic.
