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Vulcan Lies and Errors

by Joe Richardson

T'Pol Spock Tuvok Other Vulcans The "Big Lies"

"Vulcans are incapable of lying." This is a myth that was brought up by the Romulan commander in TOS: "The Enterprise Incident". The myth was refuted as soon as in the very same episode, because Spock was lying to her all the time, and most obviously when he pretended to kill Captain Kirk with the "Vulcan Death Grip". Spock repeatedly alluded to his alleged inability to lie as some sort of running gag in the TOS movies. Here, Spock consistently insisted that he wouldn't lie but only "omit" or "exaggerate" facts. Also, the myth was quoted many more times in Star Trek (most blatantly on two unrelated occasions in SNW: "The Broken Circle"). This raises the question whether Vulcans generally lie less frequently than other humanoids, or perhaps only if they were ordered to do so, and whether they may have a particular reason to be embarrassed when they are caught lying.

The following is a list of occurrences of Vulcans not telling the truth, some of which may qualify as lies. Note that in many of the cases Vulcans perhaps don't lie in a narrow sense (as a conscious deception) but one of the following rationales may apply:

They were mistaken about something they took as a fact.
They made a prediction that turned out inaccurate or premature.
They were subject to delusions.
They changed their mind about something they said earlier.
They made an ironical remark (although Vulcans are often said not to have a sense of humor either).
Facts that apparently prove them wrong may not hold up to a more thorough investigation.

T'Pol

T'Pol says "Vulcans don't touch food with their hands" before using a fork with great precision (ENT: "Broken Bow"). On the other hand, Spock can be seen eating meat with his hands around 5,000 years earlier (TOS: "All Our Yesterdays") and the Vulcans consider eating deer in the 1950s (ENT: "Carbon Creek"). In the latter case it becomes clear that eating meat is considered "savagery" however.
T'Pol plays along with Captain Archer's request that she'll tell Trip that "Rock People" were present on Archer IV when they were only imagined (ENT: "Strange New World").
After Archer suggests wine for a possible invitation to Captain Vanik, a Vulcan, T'Pol states "Vulcans don't drink wine." (ENT: "Breaking the Ice"). She drinks wine herself before telling a story in a later episode (ENT: "Carbon Creek").
A boy playing hide and seek asks T'Pol whether she has seen a girl named Nadine, upon which she tells the "truth" that she doesn't know which girl is named Nadine - although she should be aware that Nadine has to be the girl she has seen hiding in an access port (ENT: "Fortunate Son").
A Klingon ship visited by the Enterprise appears to have escape pods (ENT: "Bounty"). This is in contrast to T'Pol's statement that "Klingon ships don't have escape pods" (ENT: "Sleeping Dogs").
After the mission to the Klingon ship, T'Pol pretends that she has to extend the decontamination cycle. She apparently does this in order to be able to spend more time relaxing in the decon chamber with its pleasant absence of smells (ENT: "Sleeping Dogs").
T'Pol tells a long story about Vulcans landing on Earth in the 1950s. If it is really a made-up story then her suggestion that her ancestor was involved is not true. If it is a loose historical account then her initial explanation of visiting the site purely for geology is not true (ENT: "Carbon Creek").
After the crew all become obsessed with trivial tasks, T'Pol insists that she is unaffected. It appears that she is obsessed with the trinary star system however (ENT: "Singularity").

T'Pol's (still) voluntary mind-meld in ENT: "Fusion"

T'Pol states that she was coerced into the mind meld, which lead to her getting Pa'nar Syndrome. In fact she openly allowed it to take place initially, but it was only later that she became distressed and wanted it stopped. She never loses her commission as a result of her wording, as it's the mind-meld practice that is found offensive not the syndrome (ENT: "Stigma").
T'Pol says "I have Pa'nar Syndrome. It doesn't make a difference how I contracted it." This turns out to be untrue as she is allowed to keep her commission after a coerced mind meld is found to be the cause (ENT: "Stigma").
T'Pol is in sickbay after she complains of a headache in an attempt to avoid Movie Night. Doctor Phlox examines her, finding there is nothing wrong with her (ENT: "Horizon").
T'Pol states "I have no interest in horror movies." then shortly after watching Frankentein, she says "I'm reading biosigns on the planet. To quote Doctor Frankenstein, it's alive.". Later, T'Pol states she is looking forward to the sequel "Bride of Frankenstein" (ENT: "Horizon").
T'Pol says "We'll return what we don't use." After she and Archer raid a 21st century ATM, the money is never shown to be repaid (ENT: "Carpenter Street").
In an Orion slave auction T'Pol shouts "I'm not for sale!" She is in fact sold soon afterwards (ENT:"Borderland").
On Vulcan, T'Pol states "I am a Syrranite. We don't lie." If her other quotes on this list are counted as lies this is not true, she isn't exactly telling them the truth either (ENT: "Kir'Shara").
Trip states "I'm going to perform a cold start in less than two minutes." T'Pol says "That's not possible!" It is done just as Trip says, so it turns out possible (ENT: "Divergence").

Spock

Spock is telling himself "I am in control of my emotions... in control of my emotion.." before he breaks down in tears (TOS: "The Naked Time").
Spock states "Vulcan has no moon." (TOS: "The Man Trap"). A large moon-like body is seen in Vulcan's sky just a few years later (TAS: "Yesteryear"). "Star Trek: The Motion Picture" initially showed two moon-like bodies near what is likely to be Vulcan, although these were edited out of later releases.
In the Abramsverse, Delta Vega is so close to Vulcan that old Spock can apparently see the planet in the day sky of Delta Vega ("Star Trek (2009)"). Maybe Vulcan is the moon, Delta Vega is a quasi satellite, or they are a double planet?
Spock withholds important evidence at a court hearing on the Enterprise to ensure the ship reaches the restricted Talos IV. It is later revealed that Spock goes along with the pretense that the court exists, while it and the commodore were all imaginary so he could help poor Captain Pike (TOS: "The Menagerie").
20th century Captain Christopher notices the strange conduct and/or the female voice of the Enterprise's computer and says: "I take it that a lady computer is not routine." Spock explains it as follows: "We'd put into Cygnet XIV for general repair and maintenance. Cygnet XIV is a planet dominated by women. They seemed to feel the ship's computer system lacked the personality. They gave it one -- female, of course" (TOS: "Tomorrow is Yesterday"). Regarding Christopher's actual question Spock does not tell the exact truth because a female voice is routine.
Before he nerve pinches the Eminiaran guard, Spock says, "Sir, there's a multi-legged creature crawling on your shoulder" where there isn't one (TOS: "A Taste of Armageddon").
Spock reminds Kirk "that this is a silicon-based form of life and McCoy's medical knowledge will be totally useless." It isn't useless (TOS: "The Devil in the Dark").
Spock pretends to be a Trillium merchant to the Klingons (TOS: "Errand of Mercy").

The "Rice Picker" lie in TOS: "The City on the Edge of Forever"

After a 20th century policeman finds Spock and Kirk, Kirk is asked to explain Spocks ears "They're... actually easy to explain..." Spock adds "Perhaps the unfortunate accident I had as a child." Any accident as a child wouldn't be the cause of his pointed ears (TOS: "The City on the Edge of Forever").
After seeing Spock making something, Edith Keeler asks "What on earth is that?" Spock replies "I am endeavoring, to construct a mnemonic memory circuit using stone knives and bearskins." This is not true (TOS: "The City on the Edge of Forever").
After the challenge of a fight to the death against Kirk, Spock says "I will do what I must, T'Pau, but not with him," he still starts fighting Kirk anyway (TOS: "Amok Time").
T'Pau tells Spock "Live long and prosper, Spock." Spock replies "I shall do neither, I have killed my captain and my friend" (TOS: "Amok Time"). Spock didn't kill Kirk, he just thought he did.
After Spock reacts with extreme excitement to news that he didn't kill Kirk, Doctor McCoy says "You can't tell me that when you first saw Jim alive that you weren't on the verge of giving us an emotional scene that would have brought the house down." Spock explains "Merely my quite logical relief that Starfleet had not lost a highly proficient captain" (TOS: "Amok Time").
Spock tells McCoy, "I do not respond to hunches, no transporter malfunction was responsible for the disappearance... No known natural phenomena could have caused that beam, does that clarify the situation?" McCoy says "No, it doesn't, it's still a fancy way of saying that you're playing a hunch" (TOS: "The Gamesters of Triskelion"). If McCoy's right, Spock is incorrect about not responding to hunches.
Spock states that "History cannot be changed" (TOS: "Spectre of the Gun"). He obliviously has to change his mind after a time travel event leads to an Andorian names Thelin replacing him on the USS Enterprise (TAS: "Yesteryear").
Also, in "Star Trek (2009)", history is obviously altered because of the actions of Nero in the past. On second thought, we may discount this occurrence because for all intents and purposes, the Kelvin Timeline is a parallel universe and the history of the original timeline has not changed.

The "Vulcan Death Grip" lie in TOS: "The Enterprise Incident"

A Romulan commander says "There's an old saying, or perhaps a myth, that Vulcans cannot lie?" Spock replies by saying "It is no myth." Later in the same episode Spock pretends to kill Kirk with a "Vulcan Death Grip" and quite clearly lies about it (TOS: "The Enterprise Incident").
Spock states "I do not desire a ship of my own" (TOS: "The Enterprise Incident"). He nevertheless becomes a captain in later years ("Star Trek II: The Wrath of Khan").
On Stratos Spock says to Droxine that she awakened him, he was already awake (TOS: "The Cloud Minders").
Spock tells Zarabeth that his home is "millions of light-years away". This is quite a big "exaggeration" as even the galaxy isn't very wide compared to that distance (TOS: "All Our Yesterdays").
Kirk asks Captain Spock for a damage report while their communications are monitored by Khan Singh. Spock replies "Admiral, if we go by the book, like Lieutenant Saavik suggested, hours could seem like days." Kirk then acknowledges this. Spock tells him "The situation is grave, Admiral, we won't have main power for six days, auxiliary power has temporarily failed, restoration may be possible, in two days, by the book, Admiral." This report later turns out to be false and Saavik says "You lied!" to Spock who claims "I exaggerated" ("Star Trek II: The Wrath of Khan").
Spock tells Kirk "You ordered me to kill my brother." Kirk replies "Sybok couldn't possibly be your brother because I happen to know for a fact that you don't have a brother." Spock then admits "Technically you are right I do not have a brother... I have a half-brother." ("Star Trek V: The Final Frontier").
Spock tells Kirk "This is a new brig, Captain, it's escape-proof." Kirk asks "How do you know?" Spock answers with "The designers tested it using the most intelligent and resourceful person they could find, he failed to escape." They do escape, albeit with outside help ("Star Trek V: The Final Frontier").
Captain Spock: "There is an old Vulcan proverb: Only Nixon could go to China." This is a minor Earth event from before first contact, so is highly doubtful to be of Vulcan origin ("Star Trek VI: The Undiscovered Country").
Spock says "Klingons have no tear ducts." ("Star Trek VI: The Undiscovered Country"). Excluding part human Klingons, Worf talks about Kahless and how he "wept the oceans into existence." This suggests he had tear ducts (TNG: "Birthright").
Spock says to Captain Scott "I understand you're having difficulty with the warp drive, how much time do you require for repair?" Scott replies by saying "There's nothing wrong with the bloody thing." Spock then tells Scott "If we return to Spacedock, the assassins will surely find a way to dispose of their incriminating footwear, and we will never see the Captain or Doctor McCoy alive again." Scott then says "Could take weeks, sir" ("Star Trek VI: The Undiscovered Country").
After Scott has agreed to pretend the engine have trouble, Spock asks Valeris to "inform Starfleet Command that our warp drive is inoperative." Valeris again thinks this is "a lie?" Spock again makes up another term, this time it's "an error" ("Star Trek VI: The Undiscovered Country").
Spock says "An ancestor of mine maintained that when you eliminate the impossible, whatever remains, however improbable, must be the truth". Since Sherlock Holmes is not real, this is either a lie or someone else in his family quoted Sherlock Holmes ("Star Trek VI: The Undiscovered Country").
Spock tells Valeris "In 24 hours we will agree this conversation did not take place." Valeris replies with "a lie?" Spock says it's "an omission" ("Star Trek VI: The Undiscovered Country").
After history has been changed, Spock has to visit his past self on Vulcan, he lies to himself and others by claiming he was Selek (TAS: "Yesteryear").
Spock says "Andorians are not known for their charity" (TAS: "Yesteryear"), yet the Andorians help Earth during the Xindi War several times for no gain (ENT season 2 et al.).
While being attacked by Klingons during a Tribble infestation, Spock suggests "We could always throw Tribbles at them." Captain Kirk replies with "I thought Vulcans didn't have a sense of humor." Spock then says "They don't." (TAS: "More Tribbles, More Troubles"). Spock's statement is unlikely to be serious.
After Kirk's shirt has the words "Kirk is a Jerk" written on it, laughter erupts and Kirk says "When you all finish laughing, I'd appreciate an explanation." Spock then claims, "I never laugh" (TAS: "The Practical Joker"). Spock is seem laughing in earlier episodes (TOS: "Plato's Stepchildren", "This Side of Paradise"), albeit not on free will.
Flying through channels on the surface of Qo'noS, Spock warns Kirk that "the ship will not fit," Kirk insists it will fit. After the ship barely gets through, Kirk brags "See, I told you it would fit!" Spock however isn't sure that it qualified ("Star Trek Into Darkness").

Spock proposes to lie about Discovery in DIS: "Such Sweet Sorrow II"

Spock lies about the destiny of the Discovery, saying that the ship has been destroyed. It is also his proposal to deny the existence of the Discovery and of his own sister, Michael Burnham (DIS: "Such Sweet Sorrow II").
Spock tells Chekov that there has never been a mutiny on a Starfleet ship (TOS: "The Tholian Web"). He lies, because he knows very well of Michael Burnham's mutiny on the Shenzhou, for which she was convicted (DIS: "Battle at the Binary Stars"). But his lie falls under the ban established in DIS: "Such Sweet Sorrow II".

Side note The common definition of a mutiny requires a conspiracy, but Burnham evidently acts on her own. Technically speaking, it does not appear to be a mutiny. But her actions are called a mutiny no less than 17 times in the series, including the wording of the indictment and other statements such as by superior officers that we can expect to be reliable and accurate. There is no doubt it is indeed a mutiny by 23rd century standards, and that Spock lies to Chekov about it.

Spock pretends to be an inhabitant of Kiley 279 (SNW: "Strange New Worlds").
In TOS: "Dagger of the Mind", Spock explicitly tells McCoy that he has never performed a mind meld with a human. This retroactively becomes a lie because he mind-melds with La'an Nooonien-Sing (SNW: "Memento Mori") and his mother (SNW: "Charades").
After they have switched bodies, Spock and T'Pring maintain the impression that they are who they look like (SNW: "Amok Spock").
Spock tells Nurse Chapel: "Vulcans cannot lie. At least not in the way that humans can" (SNW: "Amok Spock").
Spock pretends to have an affair with Nurse Chapel, to get T'Pring to end their betrothal. Chapel later tells him: "Lying isn't your strong suit" (SNW: "The Serene Squall").
Pelia says "You can always count on a Vulcan's inability to lie", but more like in an ironical side note when Spock is going to steal the Enterprise and pretends that everything is normal (SNW: "The Broken Circle").
Spock explicitly tells the Klingon captain that Vulcans cannot lie, and is thereby lying (SNW: "The Broken Circle").
Spock is lying all the time when he is fully human and still pretends to be Vulcan, making up all kinds of excuses for deferring the ritual with T'Pring and for his unusual look and behavior. Technically, these are not "Vulcan lies" though (SNW: "Charades").

Tuvok

Tuvok reveals his deception in VOY: "Caretaker"

Tuvok tells Chakotay "that I was assigned to infiltrate your crew, I am Janeway's Chief of Security." This means Tuvok lied about himself and pretended to be a Maquis for a considerable time beforehand (VOY: "Caretaker").
Janeway tells Tuvok that she "spoke to your family before I left." Tuvok asks "Are they well?" Janeway replies "Well, but worried about you." Tuvok says "That would not be an accurate perception, as Vulcans do not worry." If Vulcans don't worry, why was he so concerned about his family's wellbeing? (VOY: "Caretaker").
Chakotay asks Tuvok "Can I ask you to be honest with me, Lieutenant?" Tuvok replies "As a Vulcan, I am at all times honest." Chakotay shoots back "That's not exactly true, you lied to me when you passed yourself off as a Maquis to get on my crew!" Tuvok defends his actions "I was honest to my own convictions within the defined parameters of my mission." This is hardly "honest at all times" (VOY: "State of Flux").
Tuvok misses a shot at a game of snooker and says "Perhaps the ship's stabilizers are not operating at peak efficiency" This is a made up excuse (VOY: "Jetrel").
Tuvok tells Janeway "I've observed that Captain Sulu drinks a cup of tea each morning so I thought he might enjoy a Vulcan blend." Janice Rand comes in and says "Oh, trying to make lieutenant in your first month, I wish I'd have thought of that when I was your age as it took me three years just to make ensign." Tuvok assures Janice "I have no ulterior motive." Janeway then says "You've never brought me tea." It's not certain, but it does look as if he is aiming for promotion from Sulu by being extra helpful, as Janeway doesn't get the same treatment (VOY: "Flashback").
Captain Janeway remarks "Tuvok, if I didn't know you better, I'd say you miss those days on the Excelsior." Tuvok replies "On the contrary, I do not experience feelings of nostalgia." Before adding "But there are times when I think back to those days, of meeting Kirk, Spock and the others, and I am pleased that I was part of it." It sounds like he is nostalgic after all (VOY: "Flashback").
Marayna asks Tuvok and Kim "There's a luaw tonight, you're coming, aren't you, both of you?" Tuvok replies "No" while Harry Kim says "Yes". They both join so Tuvok was wrong (VOY: "Alter Ego").
Later at the event, Marayna tells Tuvok "You're the only one not wearing a garland!" Tuvok says "It seems somewhat excessive." Then Marayna replies "I don't believe you!" A surprised Tuvok says "I beg your pardon?" Marayna states "I think you are trying to isolate yourself and make a public protest at the same time." Tuvok asks for an explanation. Marayna tells Tuvok "You didn't want to be here in the first place, being the only one without a garland sets you apart from the others, allowing you to symbolically maintain your solitude, and since everybody can see that you're the only one without it, you're letting them know that you'd rather be somewhere else." Tuvok replies "Your logic is impeccable." This suggests Tuvok's reason for not wearing the garland was false (VOY: "Alter Ego").
Takar, a hostile scientist, warns Janeway "I can kill you and your crew in an instant." Janeway replies "Go ahead, without us, you won't prevent this ship from being torn apart... and even with my crew working I say the odds of us getting through this are what, one in ten?" Tuvok then "corrects" her by adding "One in twenty, at best!" This statement from Tuvok scares Takar away and Janeway remarks "I hope you were exaggerating about those odds." Tuvok then says "I was not!" The ship survives in good condition and since his comment helped Janeway it looks like an exaggeration (VOY: "Scientific Method").
Talking to Nimira, Tuvok insinuates that he would usually communicate telepathically if it were not for the many non-telepaths in Starfleet. But Vulcans were never known to use telepathic communication among their own species, although they may be capable of it. Well, Tuvok was just speaking of himself and he may have had special training (VOY: "Random Thoughts").
Janeway asks Tuvok to distract Leonardo da Vinci with small talk. Tuvok says "Vulcans do not make small talk." Leonardo da Vinci asks Tuvok "Where exactly are you from?" Tuvok says "Scandinavia." This is a lie as he's from Vulcan, more precisely from the "Vulcanis Lunar Colony" (VOY: "Concerning Flight").
Seven of Nine asks "Am I correct in assuming that Vulcans are incapable of lying?" Tuvok replies "We are capable of telling lies, however, I have never found it necessary to do so." Then after Seven asks "You have never lied?" Tuvok adds "Only under orders from a superior officer" (VOY "Hunters"). This means he never tells Seven that he did lie, but the opposite until she asked again.
Ensign Sam Wildman when on her deathbed asks "Who's going to look after Naomi?" Tuvok replies "You should not concern yourself with that now." She is Naomi's mum and should be concerned however (VOY: "Once Upon a Time).

Tuvok activates the "photonic cannon" in VOY: "Tiner, Tenor, Doctor, Spy"

While trying to scare away the "Hierarchy" that watched the EMH's day dreams earlier, the EMH pretends to be captain and says "Activate the photonic cannon." Tuvok then hesitates before the EMH (or ECH!) says "That was an order." Tuvok then goes along with the play acting and states "Activating the photonic cannon." The cannon is not real, just something from a dream so he couldn't activate it anyway (VOY: "Tinker, Tenor, Doctor, Spy").
Tuvok shouts "I'm not a Vulcan, not anymore" when in a crazed state (VOY: "Riddles").
At Tuvok's birthday party, Janeway notes "So it's not long before you hit the big three digits?" (VOY: "Fury"). Janeway witnesses Tuvok's memory of 80 years ago when he says "I was 29 years old" on the Excelsior (VOY: "Flashback"). So Janeway knowingly makes an incorrect statement about him being less then 100 at his public celebration, but why? One possible explanation is that Harry Kim and Tom Paris were speculating about Tuvok's age, trying to get him to tell, but he wouldn't (VOY: "Alice"). So maybe Tuvok suggested Janeway not reveal how old he was. The only other explanations are that Janeway is confused or making some kind of joke.
After capturing the impostor Dala, Janeway threatens to extradite her to the Telsians. She gives Tuvok a cue to tell the prisoner about the conditions in Telsian prisons. Tuvok hesitates, but then tells Dala the following, which he makes up on the spot: "Barely habitable. Inmates often die of malnutrition before they are brought to trial. Torture is commonplace, as is disease, including several incurable forms of psoriasis." Janeway is particularly amused about the psoriasis part (VOY: "Live Fast and Prosper").
Janeway asks Tuvok "We have known each other now for how long?" Tuvok replied "Approximately twenty years." Later Janeway adds "I have always been honest with you, but you've been keeping something from me!" Tuvok then says "I don't know what you mean." Janeway says "Don't you, it took exhaustive research, sifting through teraquads of data, separating fact from rumor, but I eventually arrived at the truth." Janeway turns around with a cake and says "Happy Birthday!" Tuvok blows out his birthday candle only because "it was a fire hazard." Janeway could have been right that he was not honest with her, considering they knew each other for 20 years, and the candle was not a fire hazard in that case (VOY: "Fury").
Neelix asks Tuvok "Did I ever tell you about Salvoxia?" Tuvok replies "If I say yes, will it prevent you from telling the story?" Although not lying, Tuvok is considering doing so (VOY: "The Haunting of Deck Twelve").
When investigating a crime, Tuvok tells Janeway "I have worked meticulously, yet he has outwitted me each time!" Janeway asks "How can you be sure it's a 'he'?" Tuvok replied "I can't. But I am." This statement contradicts itself, as both can't be true (VOY: "Repression").
When Tuvok is at a First Contact Day celebration on the ship, he says "Vulcans do not dance." Tuvok does dance later on even. Before Tuvok dances, and is refusing to do so, Neelix says "But it's tradition," Tuvok then replies "There is no tradition, this ceremony is entirely your invention." Janeway interupts by adding "This is an official ship function, Commander, don't make me order you to dance!" I would doubt that Neelix invented the First Contact Day celebration, perhaps the dance but not everything else (VOY: "Homestead").
Another potential lie is when Tuvok states "Vulcans don't experience fear." But he seems to have stage fright over dancing (VOY: "Homestead").
A hospitalised Tuvok says "I know you." Janeway replied "That's right. I'm your friend, remember?" Tuvok states "You are an impostor... Janeway visits on Sunday, today is Thursday, logic dictates that you are not who you claim to be." It is the real Janeway (VOY: "Endgame").
After Bashir suggests destroying Deep Space Nine, Mirror Tuvok says "It is highly unlikely that anyone assigned to such a mission would survive." Bashir does survive the mission though (DS9: "Though the Looking Glass").

Other Vulcans

Ambassador Soval

At a meeting with Andorians, Soval says "Vulcans don't drink." Then he decides to drink for the occasion straight away (ENT: "Cease Fire").
Soval gives Tucker a data module and says "This shows the gaps in our satellite surveillance, when beam-ins can't be detected." Tucker replies "We're not exactly cleared to have this." Soval then says "Have what? All I see is a Starfleet data module" (ENT: "The Forge"). He knows it has restricted data on the module.

Doctor Yuris

Yuris tells a Vulcan hearing on T'Pol's commission that she was forced to have a mind meld "against her will" to justify her having Pa'nar Syndrome. T'Pol then complains "You gave me your word!", as he earlier promised not to tell. Even Archer, a human, kept quiet on this matter (ENT: "Stigma").

Syrran

When on the run as a fugitive, Syrran, leader of the Syrranites, lies about his name to Archer and T'Pol in the desert during a storm, he calls himself Ebdel (ENT: "Awakening").

T'Pring

Spock's betrothed wife is extremely deceitful to Spock during the ceremony, she is scheming and planning on cheating with Stonn regardless of the result from the ceremony, although she doesn't technically lie (TOS: "Amok Time").
After they have switched bodies, Spock and T'Pring maintain the impression that they are who they look like (SNW: "Amok Spock").

T'Pau

Although T'Pau doesn't technically lie, she doesn't tell Kirk that it's a fight to the death until after he agrees to it, which is deceitful (TOS: "Amok Time").

Ambassador Sarek

Sarek says "Tellarites do not argue for reasons, they just argue" (TOS: "Journey to Babel"). Although argumentative, they have reason as it's considered a sport on Tellar (ENT: "Bounty").
Sarek lies to Kirk when asked for his location during an ambassador's death, Sarek says he was "meditating" later he says he was "incapacitated" after his medical condition was discovered (TOS: "Journey to Babel").
Spock agrees with Sarek that his wife is too emotional, then asks "Why did you marry her?" Sarek replies "It seemed the logical thing to do." (TOS: "Journey to Babel"). This is contradicted by Sarek, as after her death in a timeline altered after the marriage, he says "You asked me once why I married your mother, I married her because I loved her" ("Star Trek (2009)"), so was it love or logic, Sarek?
Sarek tells Spock in disguise "You saved my son's life, Selek, there is no way I can fully repay you for that." Spock asks for him to "Try to understand your son, Sarek of Vulcan, that will be repayment enough for me." Sarek replies "What a strange request, but I will honor it" (TAS: "Yesteryear"). However, a century later when Sarek has died it's revealed they did not understand each other at all (TNG: "Unification").

Sarek crying in TNG: "Sarek"

Captain Picard tells Sarek "I saw you crying!" Sarek denies it, "I do not cry" he says. Picard insists "I was there, I saw the tears." Sarek corrects him by saying "You exaggerate, I recall only one tear." This means he did cry after all (TNG: "Sarek").

Lieutenant Saavik

After Kirk is about to beam to a risky area, Saavik states "General Order 15: No flag officer shall beam into a hazardous area without armed escort." Kirk responds by saying that "there's no such regulation." Saavik looks somewhat surprised by the reply. Either she is trying to assist Kirk by making up general orders, or Kirk doesn't remember it?

Sybok

Sybok states "The people of your world once believed the world was flat, Columbus proved it was round" ("Star Trek V: The Final Frontier"). This is untrue, the Earth was known to be round, and the length of the equator was already calculated at the time, Columbus was trying to prove that the distance between East Asia and Europe was shorter than expected, and he was wrong. It was much later that Magellan's voyage proved it was round empirically.

Lieutenant Valeris

Valeris was discovered as a traitor, so she was lying all the time ("Star Trek VI: The Undiscovered Country").
Kirk asks for names from Valeris, who replies "I do not remember." Spock claims it's "a lie." Valeris picks up Spock's technique and says it's "a choice." A mind meld finds that she does know the names ("Star Trek VI: The Undiscovered Country"). So she was lying about not knowing the names.

T'Paal

T'Paal is pretending to be Tallera, a Romulan mercenary, and is being dishonest. She reveals the truth about her identity to Picard later, but tells him she was a spy trying to "find the stone of Gol" to prevent isolationalist Vulcans from getting this telepathic weapon. In reality, it is her who is part of that group and she is planning to use it (TNG: "Gambit II").

Sakonna

The Vulcan member of the Maquis goes to Quark to buy arms. After being arrested she says to Quark that she did "the logical thing." Quark then lectures her on the third Rule of Aquisition "Never pay more than you have to." Sakonna says that's "logical" but adds she is "willing to pay any price". Quark says it's more logical to "negotiate peace" as everyone is on a level field before so it'll be cheaper to attain peace. She then looks stunned as if her logic was proven incorrect (DS9: "The Maquis").

Captain Solok

After the Niners baseball team celebrate getting a point against his Vulcan team, Solok goes and yells at Odo "Umpire, this is completely improper!" Solok adds "The game is not over!" He then realises he shouldn't be touching Odo due to game rules and Odo says "You're gone!" The game is over for him, but later Sisko says he looked "emotional" and Solok denies it despite being visibly upset that the game didn't go as expected (DS9: "Take Me Out to the Holosuite").

Ensign Vorik

Tuvok says "Lieutenant Torres is out of contact on the planet." Vorik during pon farr replies "Then I'll find her, she needs me, and I need her!" Tuvok states "It's a more sensible strategy to get her back to Voyager, and then decide on the correct resolution." Vorik insists "The resolution must be that we become mates, it's only logical!" Tuvok says "Torres has never been a great follower of logic" (VOY: "Blood Fever"). Although it appears Vorik (and Tuvok?) consider this logical, it isn't as a Vulcan woman was on board Voyager anyway (VOY: "Repression").

Data

Although not a Vulcan (McCoy wasn't sure ;-)), Commander Data is added here as he automatically assumes Vulcans cannot lie (TNG: "Data's Day"). This is important as he is an android with great intelligence and should have a valid reason before he considers that to be true.

The "Big Lies"

"Time travel is impossible"

Ambassador Soval says the "Vulcan Science Directorate has determined that time travel is impossible" (ENT: "The Expanse"). This is contradicted by many episodes, most notably when Spock performed the calculations for time travel to to the 20th century ("Star Trek IV: The Voyage Home").

High command lies

When accused of deception, as he hid his melding ability, Soval says "Deception has never been a stranger to this room" (ENT: "Awakening"). This is a suggestion the High Command frequently lies.

"Melders are a minority"

T'Pau and Archer confront the High Command in ENT: "Kir'Shara"

It is explicitly stated by physicians that only a small percentage of Vulcans are capable of mind melds because of what is seen as a genetic defect (ENT: "Stigma"). T'Pau says she could initiate the capability of melding in everyone (ENT: "Kir'Shara").

"Pa'nar is incurable"

According to T'Pau, the notion that Pa'nar should be incurable is "another lie perpetuated by the High Command." (ENT: "Kir'Shara").

Holding back technology

Vulcan claims to be Earth's ally and also claims to assist Earth's development. Archer thinks they are holding Earth back however (ENT:"Broken Bow"). Regardless, they refuse to share their technical advances in warp and tractor beams with Earth (ENT: "Breaking the Ice"). In real life, the refusal to share knowledge routinely goes along with the denial of the existence of such information.

Discovery denial

Spock proposes to Starfleet Command to keep the very existence of the Discovery, the spore drive, Control and the Red Angel under wraps, under the penalty of treason. He even decides to keep the existence of his sister Michael Burnham secret, not speaking of her to anyone (DIS: "Such Sweet Sorrow II").