A Seer is a witch or a cunning person with the power to divine future, past and present events through extrasensory perception.
Eyes are for seeing, not for being seen. That's why your kind come to me.
A Seer is someone gifted, or cursed with the power of prophecy. While witches are adept at performing divination and clairvoyance to a different degree, Seers are naturally endowed with such power. They are significantly more attuned with the psychic vibrations of the universe, and may access information through various techniques that are incomprehensible to the average witch.
Even a witch as powerful as Countess Von Marburg needed to rely on a ritualistic spell in order to obtain hidden information about Mary Sibley and the Essex Hive. Whereas, a Seer named Petrus, though considerably less powerful than the Countess, was able to learn about almost any event, future or past, through sheer will. Nevertheless, Petrus once expressed to John Hale how divination is not an exact art because, contrary to Puritanical belief, the future is not set in stone and can always change.
Powers and Abilities
Seership is an innate faculty physically linked to the eyes of a seer. A seer is able to see past, present and future events, reveal unknown identities and much more with mere willpower. Sometimes, in order to strengthen or clarify a vision, a Seer may use external resources such as ritual objects like a bowl of water, or familiars acting as extensions of their eyes.
A Seer can also share their visions with others. Displacing their eyes from their eye sockets and putting them in the hands of those who seek a vision, a Seer is able to show them glimpses of what they are looking for. Otherwise, even putting their hands close to a Seer's eyes can serve the purpose. Eating the eyes of a Seer confers seership definitively. As shown with Tituba, the full extension of this power is triggered by blindness.
John Hale: "Petrus, really. You ought to wear a little bell."
Petrus: "And you, Magistrate, need none. We heard you the moment you left the road. Come."
John Hale: "I had a bit of trouble finding the place. Seemed to recall you having been farther north last time."
Petrus: "Perhaps I was, Magistrate Hale. Eyes are for seeing, not for being seen. That's why your kind come to me. You find me when you need me. So, what do you need?"
John Hale: "Someone broke our circle in the woods last night. We need to know who saw us."
Petrus: "Ah. Full buck moon? Uh-huh. You were there that night, weren't you, little friend? Time to wake up. What did you see? Tell Mary Sibley we will find out who was in the woods last night, but it takes time."
The eyes of a Seer are the source of their power. This was proven after Tituba consumed both of the eyes that were left behind by the recently murdered Petrus and immediately developed her own second sight. Through this power, Tituba was able to discover the identity of the latest witch hunter in Salem as John Alden.
Seers are able to share their visions with others regardless of whether or not the person is a witch. This was proven after Mary Sibley sought the help of Petrus to discover the outcome of John Alden after she abandoned him in the woods. However, the vision that was seen by Mary was forged by the Indians, and while Mary believed the vision to be true, Petrus could sense that is was a lie.
"Secrets of Salem: The Seer" is a special feature video in Season One's Gallery on Salem's official website. It's a character insight about Petrus.