If you started watching Doctor Who in the 21st century (which is most of us!) you probably think the most famous catchphrases of the show are “Geronimo!,” “Allons-y!,” or, the biggest meme-maker of them all: “Wibbly Wobbly, Timey-Wimey.” But, before the long-running sci-fi show enjoyed a rebirth starting in 2005, the silly sentence most associated with the Doctor was: “Reverse the polarity!”
This line recently resurfaced in Episode 9 of Season 11, “It Takes You Away," and the history of this catchphrase is decidedly wibbly and very wobbly.
Like many famous nerdy catchphrases, “reverse the polarity” has a history of being referenced more than it’s actually said in the show. In “It Takes You Away,” the line is delivered not by the Doctor, but by Yaz (Mandip Gill) when — in a moment of universe-threatening crisis — she suggests to the Doctor (Jodie Whittaker), “Couldn’t you reverse the polarity?” To which the Doctor replies triumphantly, “You speak my language!” This joke has more than one layer, mostly because the Doctor’s reliance on this concept is mostly only a reference at this point, and hasn’t been taken seriously since the '70s.
The phrase “reverse the polarity” originates with the 3rd Doctor, as played by Jon Pertwee from 1970 to 1974. For those who may have forgotten, Pertwee was the Doctor who drove a car named Bessie, rocked a black coat with red velvet lining before Peter Capaldi, and wore the kind of lace jabot shirt later made famous by Austin Powers. The 3rd Doctor is also the guy who first used the non-violent one-touch Venusian Aikido, which Jodie Whittaker’s 13th Doctor has busted out twice this season, first in “The Ghost Monument” and again in “Kerblam!" So, for you fans who think Whittaker's facial expressions make her similar to David Tennant’s 10th Doctor, it seems like she may also really dig the 3rd Doctor, too.
But when did Pertwee’s Doctor first say “reverse the polarity”? Well, that’s where things get dicey.
In “The Terror of the Autons,” (1971) the Doctor says, “Not if we change the polarity,” which is pretty close to the catchphrase, but not quite. Then in “The Daemons" (1971) he says, “Reverse the polarity,” but only after being questioned by what he meant by just saying “reverse it.” (And to be totally clear, the 1st and 2nd Doctors were known to talk about “reversing” fields and other pseudo-science gobbledygook all the time.) So, it’s not really until we get to “The Sea Devils” (1972) where, in a conversation with the Master, the 3rd Doctor says, “I reversed the polarity of the neutron flow,” which became the most popular version of the catchphrase, and the one that stuck in the public consciousness. From that point on, Pertwee said the words “reverse the polarity” exactly four more times across three episodes, but never mentioned neutron flows ever again.
However, because "reverse the polarity of the neutron flow" is both so specific and so utterly generic at the same time, Doctor Who began sort of making fun of itself when versions of the phrase cropped up in subsequent incarnations. In Tom Baker’s first serial as the 4th Doctor, “Robot” (1975), he says: “The calculations for the reverse polarity should be child's play!” This implies of course, that his predecessor was overstating his own intelligence by constantly bragging about being able to reverse polarities all the time. (Or roughly six times total.)
Then, in Peter Davison’s first serial, “Castrovalva” (1982), the idea that Doctor Who was only going to mock this phrase was solidified. In a sort of reflective reverie, the 5th Doctor (Davison) blurts out the phrase, “Reverse the polarity of the neutron flow!” but is taken aback the second it's out of his mouth. After that, the phrase officially became an inside-baseball (or inside TARDIS) joke for Whovian die-hards and ceased to mean much in the way of actually changing (or reversing) a plot point. This kind of accidental dropping of the phrase happens again in "The Almost People" when the 11th Doctor is cloned and delivers the phrase in a decidedly Tom Baker-esque voice.
In “The Day of the Doctor” (2013), the 10th (David Tennant) and 11th (Matt Smith) Doctors both reverse the polarity of a time vortex with their sonic screwdrivers, but then jokingly realize that they are “confusing the polarity.” Finally, the 12th Doctor (Peter Capaldi) dropped the whole phrase “reverse the polarity of the neutron flow” in the 9th season episode “The Girl Who Died” (2015), where he followed it up with the quip, “I bet that means something — it sounds great.”
So, did the comeback of the phrase actually make any sense in "It Takes You Away," or was it meaningless again?
In a sense, this episode used the phrase in reference to the plot without calling too much attention to itself. In fact, this might be the first time since the '70s that having the Doctor reverse the polarity wasn't a total joke. In real science, the "polarity" of something simply refers to the relative direction of magnetic fields. So, if the Doctor reverses the polarity of something, it means she's trying to invert the direction of magnetism, or as was the case in "It Takes You Away," energy from another universe. Because the Doctor was trying to mess with a portal to a universe which seemed to have inverted properties, reversing the polarity of something in that portal makes a tiny bit of sense, if you squint.
Also, now that the Doctor is no longer played by a male actor, and has jettisoned some of its cumbersome continuity in the new season, the phrase "reverse the polarity" could have another meaning altogether. Some of the Doctor Who stories post-2013 were considered polarizing by the larger fanbase, but since the beginning of Jodie Whittaker's era, the fandom has been (with a few exceptions) reunited and stronger than ever. The new Doctor didn't inherit her sonic screwdriver from previous incarnations, she built it from scratch in her first episode. Meaning, her ability to reverse the polarity wasn't something she borrowed from the past. In a wibbly-wobbly, timey-wimey way, the 13th Doctor kind of invented reversing the polarity herself.