Telepathy

There are four types of telepathy:

• Nascent At best, a nascent telepath can sense the mood, disposition and emotions of those around them without ill effect. At worst these sensations impact upon them as an unintelligible, cacophonous and even painful onslaught, without hope of being able to block or filter any of them. Nascent telepaths rarely respond well to treatment to make it stop nor to any training that might improve upon or help them control their abilities.
• Passive A passive telepath is closer to the "mind reader" of popular imagination and they are able to perceive the thoughts of those around them, be that as coherent linguistic constructs, images, desires or emotions. Typically a passive telepath will be able to focus upon the thoughts of a particular individual and to filter or block out entirely the thoughts of others. They may, to a greater or lesser extent, be able to detect and perhaps even resist the attentions of other telepaths.
• Active An active telepath is able to proactively probe and interrogate the thoughts and memories of others; implant suggestion, alter perceptions and even control the actions of others; counteract similar actions taken against them by other telepaths; evade detection by other telepaths.
• Formative A formative telepath might, theoretically, have the ability to invade the minds of others to not only probe their memories at will but also to remove and change those memories, even to the extent of implanting entirely false memories; there are, however, no known instances where a human has been able to demonstrate such abilities.

Occurrence

Telepathy is rare: fewer than one person in a thousand has any demonstrable telepathic sensitivity or abilities; of those, most are nascent. Around a half of nascent telepaths suffer negative effects.

Side/Secondary Effects

It probably goes without saying that telepaths make amazing lovers.

Source

Telepathy is an innate ability one is born with, nothing more, nothing less. What causes it is not known although no convincing evidence has been found to suggest any genetic predisposition.