Polygraph is a placebo "eye of God watching you" to encourage confessions during interrogation. No more, no less. Like any placebo, it doesn't work (as well) if you know it's a placebo.

Either way, it's inadmissible in court. It's a technique for aiding in interrogation (like torture would be, if it worked), not a forensic technique for producing evidence.

Torture does work in cases where the information is verifiable. Consider for example that the interrogator has an encrypted file and a subject that knows the key.

Torture is morally abhorrent, but it's not necessarily ineffective.

"What's the decryption key?"

"I don't know."

I thought the placebo affect can still work (to some degree) even if you knew you were given a placebo.

https://www.health.harvard.edu/blog/placebo-can-work-even-kn...

Exactly as 3JPLW mentioned, government agencies value the polygraph as an aid to interrogation. Naïve and gullible persons, be they applicants for government jobs, criminal suspects, or criminals released on probation or parole, will sometimes make admissions that they might not otherwise make, because the fear that the polygraph can read their mind convinces them that their best choice is to confess.

But the polygraph can only have such utility so long as the general public believes that it can detect lies. We're at the point now that applicants for public jobs who face polygraph screening are often being specifically instructed not to research polygraphy.

it can give an avenue for questioning based on raised tension or whatever. its bot a complete farse but is not very dependable and can be decieved as well as false positives.

It's a useful interrogation technique, but only if the public believes it works.

Example in fiction: https://www.youtube.com/watch?v=DgrO_rAaiq0

LD tests are an unreliable technique if the subject has a clue of what LDs do measure, namely stress, and how to control those forms of stress measured by the device. After a little behavioral training, most anyone should be able to significantly reduce their stress response when lying, making the test results much harder to interpret effectively.

LDs don't catch spies. They catch novices. Aldrich Ames beat the test repeatedly. But he would, since his job was counterespionage.

They use it to ferret out untrustworthy people at government contractors. This catches some moles.

The real problem is when this hocus pocus enters the legal system and people get convicted based on examiner testimony or face the presumed guilt applied to anyone who refuses a polygraph.

There is no documented example of the polygraph ever catching a mole. On the contrary, all of the known moles who were subjected to polygraph screening beat the polygraph.

Saying that they "beat" the test gives the test too much credence. The test is a ploy to make the subject confess. The only step to beating the test, is the simple knowledge that it's a ploy in the first place.

Point well taken. But the U.S. government does consider the polygraph to be a pass/fail procedure. Applicants and employees suffer severe career harm for "failing."

Wasn't Philby caught by polygraph but argued his way out of the results? (He was, in fact, a spy all along).

No, Philby was not "caught by polygraph."