The one ahead principle is a foundational mentalism technique that allows the performer to stay one step ahead of the audience during a routine. By secretly acquiring knowledge of one piece of information in advance, the mentalist can use this knowledge to convincingly predict or reveal subsequent pieces of information while appearing to demonstrate extraordinary intuition or psychic ability. The one ahead principle is employed in prediction effects, mind-reading routines, and divination tricks.

The one ahead principle works by shifting the perceived sequence of events. For example, as the performer writes down a “prediction,” they are noting information revealed mere moments earlier by the participant. This process is repeated, with each new “prediction” being based on previously acquired information, creating the illusion that each revelation is made in real time. Applications of the one ahead principle include mind-reading routines with sealed predictions, billet readings, card divinations, and the classic mentalism effect Mental Epic. When executed skillfully, the one ahead principle is nearly impossible for an audience to reconstruct, making it a versatile and powerful method in mentalism.