Why didn't Vader detect the Force in Leia?

Question

In the original trilogy of Star Wars, one of the first scenes is Leia meeting Darth Vader, as Vader is asking her where the plans for the Death Star were hidden. Leia claims ignorance and says that she is on a diplomatic mission to Alderaan. Leia was right in front of Vader. And yet, Vader didn't sense that the Force was strong with her.

Disclaimer 1: This question is not asking how he didn't realise through the Force that Leia was his daughter. Daughter or not, the Force was strong with Leia. Why didn't Vader sense that?

Some writings I've seen say that Leia never had any Force-training. And Luke was only sensed by the emperor after training with Obi-Wan and starting to use the Force. But in many instances in the Star Wars legends, and even in the first movie Phantom Menace, many other children, including Anakin were detected to be Force-sensitive without having training. That's how they single out prospective Jedi and begin training them from a young age. With Leia, it must have been even easier to sense that she was Force-sensitive, because the Force was so strong with her and Luke.

So why didn't Vader sense that she was Force-sensitive?

Answer 1

Just because he didn't say that magic phrase "the Force is strong within her" does not mean he didn't sense it. Also, it's entirely possible he uttered those words in some interaction not in a scene we saw. They didn't claim to follow his every utterance, 24/7.

I'd say evidence points to the fact that he did sense it. She didn't give up what she knew just being in the room and under the influence of his Sith powers/Jedi mind-tricks. She withstood the torture-bot without giving it up. I'd think that threatening and then destroying her home planet (by Tarkin) would be an indication that Vader found her to be quite formidable and was stymied.

Her resistance to the mind probe is considerable. It will be some time before we an extract any information from her.

That seems to be a pretty close equivalent, and, really, would a Sith openly admit to his supervisor about being matched in the Force by some untrained person?

Answer 2

In the canon Star Wars book, The Princess, the Scoundrel and the Farmboy (by Alexandra Bracken) during Leia's interrogation, we are told that Leia senses some surprise from her interrogator (Vader):

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There was...power behind each of his words. They nudged at her. They prodded as sharply as any knife. So Leia did the only thing she could--she pulled back. Physically, toward the wall. Mentally, to a place the voice couldn't find her, a protective blanket that didn't let any of the darkness nudge through. The freezing pressure on her mind was thrown back. The rumbling voice made a sound of surprise and was quiet for a long moment.

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Vader stepped back, watching her as still and silently as any poisonous snake about to strike....."Careful," Vader warned. "If you continue to resist, soon you will be neither."

In this scene, it is clear that Leia used the Force to resist the probe to an extent and that her interrogator (Vader) sensed this, resulting in his surprise and silence. Vader might not known of her force sensitivity until this scene. But I am sure he knew after the events of A New Hope.

As for a familial bond, it has been quite clear that Leia had more of a bond with Padme than Anakin (who has more of a bond with Luke). This is made clear with Leia's "memories" of Padme in Return of the Jedi, and several examples in the comics where she sees Padme's protrait turn and stare at her and feeling cold in the Naboo Palace where Maul once stood, implying she feels her late mother's feelings at that time. Due to this, Vader might not of known as strongly of a connection with Leia. This is evident as he never mentions Leia's name even when the revelation is made known to him that he has a daughter:

Return of the Jedi script

VADER:...especially for...sister...so you have a twin sister. Your feelings have now betrayed her too. Obi-Wan was wise to hide her from me...now his failure is complete. If you will not turn to the dark side, then perhaps she will.

VADER: You were right about me. Tell your sister... you were right.

Vader's knowledge seems to be a be limited when it comes to his daughter/Leia, but because we, the audience, know who Luke's sister is, we assume he must know who she is. However, when you really look at it, the two don't have much interaction and when they do, the two don't exactly see eye-to-eye.

But he did sense the force in her during the interrogation but probably thought nothing of it as she was to be terminated during the events of the film; (she also was involved in the Rebellion and hence, a traitor).

Answer 3

A few reasons

1. Leia was neither strong, nor proficient in the Force. The only reason Luke reaches her is because she is his twin. We don't see her use the Force anywhere else. Note that she didn't detect Vader was her father either.

2. We see Vader only able to detect people actively using the Force, and in some close proximity. So Obi Wan on the Death Star (probably enhanced due to the sensation being familiar) and Luke in his X-Wing reaching out with his limited skills. Likewise, Snoke detects Rey only after she begins to use her Force skills.

3. He wasn't expecting anyone else to use the Force. She's a rebel spy and he needs intel. So he probably wrote her resistance to the mind probe off as having a strong will. He was also angry when he was confronting Leia, which probably overshadowed any hints he could have gleaned by reaching out to her with the Force..

So why could Qui Gon detect Anakin? Young Anakin (and even Rey in TFA) was an intuitive Force user, meaning a Jedi or Sith could detect them with the Force. We also don't see Vader use any Force based interrogation (like Kylo Ren did). It's likely neither he, nor Palpatine knew of any such technique.

Answer 4

I think George Lucas hadn't planned on Leia being Luke's sister until ROTJ. The dialogue between Leia and Vader in A New Hope seems as if they are familiar with each other. Also Luke looking at her as a love interest in New Hope and ESB. I think Lucas was trying to top the big surprise of Vader telling Luke he was his father in ESB by making Leia his sister in ROTJ. I know Yoda tells Obi Wan that "there is another" in ESB. But I think he might have originally referring to the possibility of Anakin turning back to the light side of the Force. Also Obi Wan doesn't seem to recognize Leia as Luke's sister in A New Hope. He was there when she was born and made arraingements with Bail Organa and Yoda in ROTS. Yet he doesn't seem to recognize her or C3PO or R2.

Answer 5

Force sensitivity is not simply genetically inherited. Yes, there are some families where Force is strong. Beside Skywalkers, we could mention family of Mother Tarzin, Darth Maul and Savage Opress. On the other hand, we have powerful individuals who came from non-Force sensitive families ( Palpatine, Darth Bane in Legends etc ) . Also, even in families where Force runs strong, some members are more attuned to it then others. Maul was stronger than his brohter Opress, and Opress was stronger than Feral (whom he killed) .

Back to our question, it is quite possible that Leia was Force sensitive, but far bellow the level of Luke. She could have inherited that from her mother Padme Amidala who was not strong in the Force as her father Anakin/Dath Vader. So, when he questioned her, he did sense something (previous answer nicely quotes "The Princess, the Scoundrel and the Farmboy" ) but it was not that extra ordinary. Galaxy is large, there are many Force sensitive beings, but very few qualify to be in same league as Darth Vader or Palpatine. In old times, Leia could become average Jedi. But two reigning Sith lords didn't have need for average. Leia was to be tricked to fly to secret Rebel base, and later she would have been destroyed.

On the other hand, both Palpatine and Vader recognize the treat that Luke brings to their rule . At that point in time ( Empire Strikes Back) "he is just a boy", but "he must not become a Jedi". Obviously, Luke's powers are not great (they are below average Padawan from Old Republic ), yet both Sith lords feel his potential . This leads to conclusion that Leia was not as strong in the Force as Luke, and therefore Vader didn't pay much attention to her .