The Power of Three is the collective power of the Charmed Ones, said to be the strongest kind of magic that has ever and will ever exist in this world. The requirement to tap into this power is for each witch to possess one of the three following powers: Telekinesis, Molecular Immobilization, and the power of Premonitions.
While most of the spells written in the book require the Power of Three to take enough effect, it isn't always necessary for all three sisters to chant a spell together as long as they are all together at the same time. For example, Phoebe cast a spell to awaken their powers as the Charmed Ones by herself and was merely in the vicinity of her other two sisters; Piper summoned the Power of Three to save Paige from an invading spirit, and Paige summoned it to vanquish a Slime Demon.
It is not explicitly stated how a Power of Three bond is formed, but prophecy, lineage, identity, and mutual trust seem to be key factors. It could be possible that the three must take a blood oath as a promise to always remain together, or something of that nature, as Phoebe mentioned that she and her sisters once took one to always remain friends prior to becoming witches.
It may also be that one needs the aid of a spell to create such a bond. Phoebe read a spell to bestow the power of the Charmed Ones upon the sisters that is titled "Dominus Trinus":
Hear now the words of the witches,
The secrets we hid in the night,
The oldest of Gods are invoked here,
The great work of Magic is sought.
In this night and in this hour,
We call upon the Ancient Power.
Bring your powers to we sisters three!
We want the power!
Give us the power!
Triangle of Power
Evil beings have also been seen to exploit the Power of Three. For example, the Rowe Coven was a trio of two warlocks and one half-Warlock (just as the reconstituted Charmed Ones were made up of the witches Piper and Phoebe and the half-witch, half-Whitelighter Paige), making them the evil equivalent to the Charmed Ones.
Pros & Cons
The effect of a Power of Three bond being formed is that all the members' powers are pooled together into a collective. One of the benefits of this bond is High Resistance—the ability to withstand high levels of magical force that would kill an ordinary person.
More powerful (and hence higher level) beings are harder to kill/affect with one's powers than lower-level ones; for example, Piper and the other various Charmed Ones have been shown to have taken direct hits from all kinds of attacks such as fireballs and energy balls and have survived them many times over, whereas such attacks would instantly vanquish any other magical creature. The Triad is also highly resilient to Piper's combustion power whereas other lower-level demons usually disintegrate within seconds. Therefore, this particular con is easily balanced out by the strength gained by their collective.
The amount of power one gains from this bond is relative to the level of the other beings involved, though, in the case of Prue, Piper, and Phoebe, they were all more-or-less equal in strength when they first received the Power of Three.
Another downside of this is that if one member dies the rest of the collective will be weakened, making the other members easier to kill off with the death of each member.
There is the fact that this collective magically links all of the members to each other in various metaphysical ways. Certain spells cast on one member may affect the others through this connection, such as when Prue was magically turned into an evil warlock through a Dark Wedding ceremony, which subsequently caused Piper and Phoebe to turn into Warlocks as well.
Additionally, the Power of Three bond can be broken in several ways. If the members use their powers on each other in a negative manner or atmosphere, then the bond will be broken. Fortunately, this bond can be reforged by all three of the members reconnecting with each other on an emotional level or something to that effect. For example, when the Charmed Ones intentionally used their powers on each other during an argument, which shattered their Power of Three. However, later on, they forgave each other for their actions, showing an understanding of the others' point of view and demonstrating their solidarity as sisters (which is where their Power of Three comes from) in a battle against a demon; as a result, their bond was restored.
The bond can also be broken in a more permanent way if one of the members dies. Although the strength of their power increases their chances of not being killed in battle, it is still possible, and such a death could have severe implications for the bond since the collective would be damaged beyond repair. In the case of the Charmed Ones, this was miraculously solved by the revelation that they had a half-sister, Paige Matthews, whose lineage as a Halliwell witch (as well as Whitelighter heritage) allowed the Charmed Ones' Power of Three to be reconstituted. However, this event is incredibly unlikely under normal circumstances.
The first time that the term Power of One was mentioned was in the episode The Wendigo. The Power of Three was also once referred to as the "Power of One" to describe how all three Halliwell sisters work as one.
The term Power of Four was coined by the Phoebe Halliwell from an alternate universe where the balance of power was shifted towards evil.
The term described the collective powers of Paige, Phoebe, and their evil counterparts from the alternate universe, and was shown to be weaker than the Power of Three when they're not able to finish Gideon off by themselves. However, this may be at least partially due to the fact that there were only two Paiges and two Phoebes and no Pipers to finish off the trios.
The four witches tried to invoke the Power of Four with the following spell:
We call upon the Ancient Lore
To punish with the Power of Four,
Strike down this threat from both there and here,
Make him suffer, then disappear.
- The 'Power of Four' was used in "It's a Bad, Bad, Bad, Bad World, Part 2".
- Several times throughout the show the term "Power of Two" had been used when one of the Charmed Ones was separated from the other two. However, this was not intended to literally mean that; for a short time, the Charmed collective was diminished, though it cannot actually be hindered by distance—it merely means that only two were present to actually apply their powers and do what was required.
- There had been certain hints throughout the show that Billie and Christy Jenkins's sisterly bond resulted in a Power of Two-like effect, and that, combined with their own individual powers, was what made them so strong.
- On one occasion ("Forever Charmed") the "Power of Three" consisted of Penny, Patty (through fetus Phoebe), and Piper's combined power of three generations to banish the Hollow and get it back in his container box.
- Any three people possessing each of the Charmed Ones' powers through their blood, or a "To Call a Witch's Powers" spell, for example, were able to form their own Power of Three, provided they could stop the original users from channeling it in the first place. The Stillman Sisters, Patra, Pilar, and Phoenix exploited this for their own ends. In Season 2, three monkeys were injected with the sisters' blood and given their powers; and presumably obtained the Power of Three as well, but they never used it.
- At one point during the show, all four actresses had it written in their contracts that they wouldn't have to say the Power of Three Spell too often.
- The Power of Three Spell was last used in "The Power of 300".
- In Season 9, the Council of Elders used their abilities of divine intervention to alter the prophecy of the Twice-Blessed Child, which concerned Piper's oldest son, Wyatt. They made it so that her two other children, Chris and Melinda were twice-blessed as well, and even went so far as to give Melinda unnatural Whitelighter abilities so that in the future, the three eldest children of the Charmed Ones would inherit a more potent form of the Power of Three and be an even greater force of good than the Charmed Ones. Their interference was absolved by the Angels of Destiny. The Angels then revealed that if Piper or Phoebe's kids were to ever inherit the Power of Three it would be under natural circumstances, such as if evil gained the upper hand, and not because of external forces interceding.
- The term "The Power of Three" has been used as inspiration for many Charmed titles:
- "The Power of Two" and "The Power of Three Blondes" both played on this term.
- The final issue of the Season 9 comics was titled "The Power of 300". Additionally, The Power of Three was also the title used for the first book in the Charmed novels series; a novel adaptation of the pilot episode, "Something Wicca This Way Comes".
- Other television shows have mimicked this term:
- In the show "Wizards of Waverly Place," the Russo children—three wizards—used a "Power of Three" to vanquish their enemy. This is an obvious nod towards Charmed, with both shows having some similarities.
- A similar term was used in the movie "Return to Halloweentown," where three members of the Cromwell family of witches (Marnie, Dylan, and Gwen) combine their powers to "destroy" a magical amulet created by three of their ancestors.
- In season 5 episode of The Vampire Diaries, a witch named Quetsiyah utilized the blood of three Petrova doppelgängers for a powerful spell to turn her descendant into the Anchor of the Other Side—a realm that trapped dead supernatural beings. While casting the spell, the women's blood came together and formed the triquetra symbol.
- Many Charmed fans theorized that had Prue, Piper, Phoebe, and Paige all known each other while Prue was still alive and had connected with each other, it would have led to a Power of Four and made them stronger than ever.