Polygraphs are already used in other aspects of law

The argument

The objection to polygraph evidence is usually framed as a question of reliability, but proponents of this position note that institutions with real stakes already treat the technology as reliable enough to act on. Many organisations use polygraph testing as an effective tool for investigating potential misdeeds, and several of those uses sit squarely inside the legal and enforcement systems to which courts belong. In Singapore, the Football Association uses polygraph tests to combat match-fixing and has seen promising results — a setting where the consequences for those tested, and for the integrity of the competition, are substantial. In the United Kingdom, the probation service uses lie detectors to monitor sex offenders released on parole, checking whether they are breaching the terms of their release. Seven police departments across England and Wales currently use them and maintain their effectiveness. The last two examples carry particular weight here. Parole monitoring is not a private matter but an exercise of state power over an individual's liberty, and decisions taken on the strength of a polygraph result there can return someone to custody. A state prepared to restrict freedom on that basis has already accepted the instrument as probative. Police forces that retain it after years of operational use have effectively tested it against their own practical requirements and kept it. There is an inconsistency in accepting all of that while refusing the same evidence in a courtroom. Either the technology yields information worth relying on — in which case a court, with its rules of evidence, its capacity to hear challenges to the method and its power to weigh a result against everything else before it, is the setting best equipped to handle that information — or it does not, in which case the parole and police uses cannot be justified either. Since polygraphs are already used in other aspects of law, they should be allowed in court.

Context

Lie detectors are already used in the construction of plea deals, monitoring convicted criminals released on probation, and within the governing bodies of several sports including deep-sea angling and natural bodybuilding and football.

Premises

Counter-arguments

Just because some organisations are using polygraph tests to police their fields does not mean they should be used in the legal sphere. There are plenty of organisations that have publicly denounced polygraph testing and eradicated them from their governing processes. There is also a big difference between the implications of a false lie detector result for those on probation, or from a sport's governing body, versus those in court for the first time. Consider a false positive reading for a criminal that is on probation. The criminal has already been convicted of a crime. They have been released early on parole for good behaviour. The implication of a false positive on a lie detector test would see them return to prison to finish their original sentence. While this is an injustice, it is a far less serious injustice than a law-abiding citizen being locked up for a crime they didn't commit based on a false positive lie detector result. The Employee Polygraph Protection Act (EPPA) banned private sector employers from using polygraph tests on job candidates due to their wild inconsistencies. Why would we want to make something admissible as evidence in court that is not even accurate enough to use in the candidate vetting process for a job?

Rejecting the premises

[Rejecting P2] The stakes are far lower when considering whether someone should be banned from a sport of returned to prison for breaching their parole than when considering someone's original guilt from innocence. [Rejecting P4] When the stakes are so high, the outcome of a criminal trial should not be impacted in any way by the results of a polygraph test.