Truth-Default Theory (TDT) is a framework developed by communication scholar Timothy R. Levine to explain how and why people tend to presume honesty in communication. ABC is a pneumonic to guide investigative interviewers to assume nothing, believe nothing and check everything.
In essence, TDT posits that humans are “wired for truth” we default to believing others unless we have a specific reason to suspect deception. The presumption of honesty shapes interviewers’ behavior with truthful vs. deceptive subjects. An awareness of TDT requires strategies (informed by both research and practice) to overcome TDT’s limitations in detecting deceit.
Understanding Truth-Default Theory (TDT)
TDT’s central premise is that honest communication is the human default state. Most people tell the truth most of the time, and correspondingly, listeners generally assume what they hear is truthful. Levine explains that we “passively accept incoming communication as honest unless [we] have a reason to suspect otherwise.” In everyday life, the possibility that someone is lying often “does not even come to mind” absent a trigger. This truth-default state (also known as truth bias) is not a flaw but an adaptive feature of human communication. If we approached every interaction with skepticism, normal social exchange would become slow and dysfunctional. Instead, assuming honesty allows society to function smoothly, for example, we typically trust a store clerk about a price without interrogating whether they might be deceiving us. Since most people are truthful in most situations, the default presumption of honesty usually serves us well.
However, the truth-default makes humans vulnerable to deception. Because we aren’t actively looking for lies, a clever deceiver can exploit our trust. Research consistently finds that untrained people detect lies only slightly better than chance – around 54% accuracy in lab studies. This slight edge above 50% (coin-flip accuracy) is largely driven by the fact that people correctly identify most true statements, while misses occur on lies – a pattern known as the veracity effect. In other words, truth-tellers are believed more often (and correctly so), but liars often “fly under the radar” because listeners default to truth. We typically only catch lies when something “triggers” our suspicion and breaks us out of the default-to-honest mindset. A good example of this effect can be found in the “Queen of Cuba” story where a Cuban spy was not detected because everyone just believed she was not a liar.
Levine describes several trigger events that can prompt doubt: if a communicator’s story has glaring inconsistencies or lacks coherence, if their behavior seems flagrantly unusual, if we spot a clear motivation for them to lie, or if external information contradicts their claims. Any of these triggers can alert the listener that deceit is possible, at which point we shift from passive acceptance to a more skeptical, analytical mode. Notably, absent such triggers, people often don’t consider the possibility of deceit at all. Thus, TDT explains why “the best lies are never detected” – skilled deceivers avoid raising red flags, allowing the truth-bias to persist.
TDT also challenges earlier notions that there are reliable nonverbal “tells” of lying. According to Levine, trying to read body language or facial expressions is largely ineffective for detecting deceit. Many so-called cues (e.g. avoiding eye contact, fidgeting) are misleading – liars can appear confident and friendly, and truth-tellers might seem anxious or hesitant. TDT argues that how a person “comes off” is not a reliable indicator of honesty. Instead, content and context matter more. Effective deception detection, in Levine’s view, comes from “listening to what is said, not how it is said” and corroborating information rather than from observing demeanor. In summary, Truth-Default Theory explains that people naturally assume honesty in others’ communication because doing so is efficient and normally benign – but this leaves us susceptible to lies, unless suspicion is actively triggered by something that jars us out of our default trust.
Presumption of Honesty vs. Suspicion
Investigative interviewing presents a special case of TDT because the stakes are higher, and deception is more common than in everyday chat. Police officers and investigators might believe they are constantly lied to – and indeed suspects often have strong motives to lie (to avoid prosecution, protect accomplices, out of fear or shame, etc.). Intuitively, one might expect professional interrogators to be immune from truth-bias, remaining skeptical of everything a suspect or witness says. Investigators are human too, and they must fight against the same truth-default as anyone else. Even when trained to spot deception, an interviewer can be lulled by a plausible story if nothing overtly raises suspicion. TDT reminds us that unless an officer has clear reason for doubt, they may “passively accept incoming communication as honest”, just as any person would. In practice, this means a smooth-talking deceptive subject, especially one who blends lies with truthful details, can be quite hard to catch in the moment. Empirical studies bear this out: even experienced law enforcement personnel rarely do much better than 50/50 at judging veracity in real-time interviews. Truth-default often prevails until evidence to the contrary emerges. Indeed, investigators frequently discover lies after an interview, when they check facts or review recordings, rather than during the conversation itself.
On the other hand, investigators also learn to be cautious about over-suspicion. Levine notes that defaulting to truth is adaptive – it wouldn’t make sense to treat every single statement from an interviewee as a lie by default. Constantly assuming deception can backfire: “searching for lies in predominantly truthful communications may lead to disbelief of a genuinely truthful person.” In other words, an interviewer who treats everyone as lying risks misjudging honest witnesses or victims, damaging rapport and potentially missing vital information. A critical balance must be struck between healthy skepticism and an open-minded, truth-default approach. TDT suggests investigators should remain aware of their natural trust bias yet also recognize that most interviewees (especially victims and witnesses) are telling the truth. The goal is to stay alert for specific clues or evidence of deceit (triggers), rather than indiscriminately doubting everything or blindly trusting everything.
The ABC Principle: A Practitioner Strategy Against TDT
One practical and memorable way to counteract the effects of Truth-Default Theory (TDT) in investigative interviewing is through the ABC mnemonic:
• A – Assume nothing
• B – Believe nothing
• C – Check everything
This guidance serves as a cognitive and procedural anchor for interviewers navigating the truth-default bias. It encourages professionals to resist the natural inclination to accept statements at face value and instead adopt a structured, verification-focused mindset throughout the interview process.
A – Assume Nothing
The “assume nothing” directive warns interviewers against jumping to conclusions based on appearances, stereotypes, or early impressions — whether those assumptions suggest truthfulness or deception. TDT tells us that our cognitive bias will often fill in missing information with assumptions of honesty, but doing so risks overlooking key inconsistencies or missing red flags. By intentionally suspending assumptions, the interviewer remains open to the full range of possible explanations and evidence, allowing for a more objective evaluation.
B – Believe Nothing
“Believe nothing” echoes TDT’s insight that people are not naturally suspicious and tend to believe what they hear — unless prompted otherwise. This doesn’t mean that interviewers should distrust everyone, but that they should withhold belief or disbelief until claims are tested. It’s about remaining neutral and mentally bracketing the issue of veracitywhile gathering information. This protects against both over-trusting deceptive individuals and unfairly disbelieving truthful ones based on flawed intuitions or unreliable cues.
C – Check Everything
The final and most critical step “check everything” operationalizes how to move beyond the truth-default. This principle emphasizes corroboration and verification of the information provided in interviews. Every significant detail alibis, timelines, claimed witnesses, physical evidence should be subjected to scrutiny. This aligns directly with TDT’s assertion that lies often go undetected unless evidence triggers suspicion. By making verification standard practice rather than a reaction to overt doubt, investigators mitigate the risk of being deceived by convincing liars
Interviews with Truthful Subjects
When interviewing a truthful person, truth-default bias facilitates a better interaction. Presuming honesty helps build rapport and encourages the interviewee to open, because they feel believed and respected. The interviewer who listens and accepts the account (absent contradiction) will gather a more complete narrative from a truthful subject. This aligns with the information-gathering approach favored in modern investigative interviewing, where the goal is to get the whole story rather than to trip the person up. TDT reinforces that most of the time, especially for cooperative witnesses and victims, the presumption of honesty is correct. The interviewer can focus on understanding and clarifying details instead of interrogating veracity.
That said, investigators must remain vigilant for the rare falsehood even from a generally truthful person. If something the interviewee says doesn’t add up (for instance, a timeline inconsistency or an improbable detail), it should trigger follow-up questions. Under TDT, the interviewer should “ABC” the information. An honest subject usually won’t mind efforts to corroborate their story – in fact, truthful individuals often welcome providing verifiable details to support their account. For example, a truthful alibi witness might happily give specifics like “I paid for our meal with my credit card at 7:45 PM” knowing investigators can check the receipt. As TDT predicts, people with no reason to lie typically default to honesty, and an investigator can operate on that default while still methodically checking key facts. Problems arise only if an officer either uncritically accepts everything without any verification, or conversely if they unjustly accuse a truthful person of lying. The former risks missing a deception; the latter erodes trust and could cause an innocent person to appear nervous or defensive (potentially creating a false appearance of deception). Awareness of TDT helps interviewers navigate this by treating truthful interviewees with baseline trust and respect, yet remaining ready to probe deeper should a red flag surface.
Interviews with Deceptive Subjects
Interviewing a deceptive suspect is where the pitfalls of truth-default become most apparent. A dishonest subject typically tries to exploit the interviewer’s presumption of honesty for as long as possible. As Levine notes, “the best lies are never detected” at the time – skilled deceivers weave lies into credible narratives that avoid obvious triggers. An investigator who is in default “truth mode” may initially accept the suspect’s story, allowing the liar to gain confidence. In fact, many deceptive individuals prepare a “lie script” in advance. They rehearse answers to expected questions to sound convincing. If the interviewer’s questions remain routine or expected, the liar can smoothly deliver their scripted falsehoods without raising alarm. Because humans tend not to presume deceit without cause, a liar who doesn’t slip up can temporarily maintain the interviewer’s trust. This dynamic explains cases where suspects convincingly proclaim innocence in an interview and are not caught until later evidence exposes their lies.
TDT manifests in such scenarios as a sort of grace period that liars enjoy – until something breaks the truth-default state, the liar’s statements will be given the benefit of the doubt. However, once a trigger event occurs, the situation changes. For instance, if the suspect’s story lacks internal coherence or contradicts known evidence (a Trigger Sign in TDT terms), the interviewer’s truth-bias will be disrupted. The investigator should now shift from accepting mode to ABC mode, asking for fine grain detail to elicit checkable facts or provable lies. Regardless of the source, once the interviewer exits the truth-default state and actively considers that deception is occurring the liar’s advantage dwindles; they may double down on lies, but the interviewer is now actively looking to verify and will be harder to fool. Many experienced investigators describe seeing this shift: an interview might start conversational and trusting, but the tone changes the moment the detective catches a lie or a contradiction.
Importantly, TDT predicts that without such triggers, deceptive individuals can often escape immediate detection. This is why standard, non-confrontational interviews alone are poor lie detectors – a crafty suspect can stick to their story and, if nothing obviously “wrong” is noted, the interviewer’s default may remain truth-belief. Indeed, research indicates that “lies are often uncovered once the interview is over and reviewed” with external evidence. A classic example is when a suspect provides an alibi that initially sounds plausible; only after the interview, when police check CCTV or phone records, do they find the alibi was false.
In sum, during investigative interviews truthful subjects can benefit from truth-default (they’re believed, as they should be), whereas deceptive subjects benefit until something triggers suspicion. TDT influences both scenarios: it encourages rapport and information flow with honest interviewees, but it can inadvertently shield liars if interviewers aren’t careful.
Overcoming TDT’s Limitations in Deception Detection
Because truth-default can lull interviewers into missing deceit, both academics and law enforcement practitioners have developed strategies to counteract this bias while interviewing. Below are evidence-based techniques and practices designed to improve deception detection without sacrificing the positive aspects of truthful communication:
• Adopt an Information-Gathering Interview Style: Rather than beginning with accusations or trying to spot lies from demeanor, investigators are advised to ask open-ended questions that prompt detailed narratives. This approach aligns with the PEACE model used in the UK and “science-based interviewing” methods. By encouraging a subject to talk at length, the interviewer maximizes the fine grain detail available to vet. Open questions (e.g. “Tell me everything that happened that night”) are like an essay test for the interviewee, whereas yes/no questions are like multiple-choice. It’s much easier for someone to lie with a simple “yes” or “no” than to maintain a complex lie in a free narrative. An information-gathering approach exploits that difficulty. As one law enforcement guide notes, “most lies are discovered after the fact by verifiable evidence,” so the goal is to collect as many details as possible for later corroboration. This approach also naturally counters truth-default vulnerability – the interviewer isn’t explicitly judging truth vs. lie in the moment but rather treating all information as pieces of a puzzle to be checked. This mindset helps overcome the passive acceptance of statements; every claim is noted and can be verified independently. Notably, focusing on information gathering also prevents prematurely labeling a truthful person as deceptive, since the interviewer is asking for information rather than challenging honesty.
• Ask Unexpected Questions: Research shows that liars often rehearse answers to anticipated questions, but they struggle when confronted with something they didn’t prepare for. Investigators can leverage this by posing out-of-the-blue queries or changing the chronological order of questioning. For example, after a suspect gives a chronological account of their evening, the interviewer might jump back with a specific, unanticipated question: “By the way, which arm were you carrying your groceries in when you entered your apartment?” A liar who fabricated a generic story may be caught off guard, whereas a truth-teller, relying on actual memory, can answer consistently. Aldert Vrij and colleagues call this tactic imposing cognitive load on the interviewee – one method is asking them to recount events in reverse order. Telling a story backwards is hard for everyone, but truth-tellers tend to add more fine details when doing so (because they are recalling what truly happened, just in a different order), whereas liars often falter or contradict themselves. Another study found that liars provide fewer sensory and spatiotemporal details (time, location, sounds) in their accounts. Thus, unexpected and detailed questions can magnify the differences between honest and deceptive responses. Practically, an investigator might suddenly ask a suspect to draw a map of where they went or inquire about an innocuous detail that wasn’t mentioned. Truthful interviewees might be surprised but will do their best to comply (since they want to help establish the truth), whereas deceptive ones often “flounder” or give vague answers when surprised. This tactic effectively triggers liars into revealing signs of inconsistency, countering the truth-default by actively probing for verification points.
• Explicitly Elicit Verifiable Details (The “Liar’s Dilemma”): One powerful technique is to explicitly ask the interviewee for details that can be checked against evidence – names of people they interacted with, receipts or digital records, exact times and places, etc. This is known as the Verifiability Approach (VA) in deception research, which assumes truth-tellers will freely offer checkable details, whereas liars will either avoid them or risk exposure if they fabricate them. For example, an investigator might instruct, “Include any details in your story that we could later verify – like CCTV cameras you saw, text messages you sent, or people who can confirm your whereabouts.” This request puts liars in a bind – a “liar’s dilemma”. If the liar provides specific verifiable details and those turn out false, the lie will be conclusively revealed; if the liar refuses to give any verifiable detail, their story remains uncorroborated and thus suspicious. Studies show that truth-tellers usually give more verifiable information than liars do. In practice, an innocent suspect might say, “You can check the store’s security camera – it’ll show I was there at 9pm,” whereas a liar might vaguely say “I went for a drive” with no specifics. By instructing all interviewees to help provide evidence for their story, investigators make it harder for liars to hide in the truth-default. Either the liar gambles by lying with verifiable specifics (which evidence can later disprove), or they provide a sparse account that marks them as potentially deceptive. This approach has been shown to improve lie-detection accuracy in experiments. It flips the script, so the burden is on the subject to demonstrate truthfulness, rather than on the interviewer to sniff out lies from demeanor. Many agencies now incorporate this into interview protocols by asking questions like “Who else knows about this?” or “How can we confirm what you’re telling me?” early in the interview. Such questions serve as gentle prompts for honest subjects (who often willingly suggest evidence) and as tripwires for dishonest ones.
• Strategic Use of Evidence (SUE): Investigators are trained not just in what questions to ask, but when and how to deploy evidence during an interview. The Strategic Use of Evidence technique involves withholding known evidence initially, to first get the subject’s untainted story, and then revealing the evidence at strategic points to test the story. Research shows that this strategy significantly boosts deception detection rates above chance. For example, detectives might have security camera footage of a suspect at a crime scene, but they start by asking the suspect to account for their whereabouts without mentioning the footage. A truthful suspect will tell the truth (perhaps even mentioning being at the scene if innocently there), whereas a lying suspect may deny being there. When the interviewer later confronts the liar with the video evidence, the liar is caught in a blatant falsehood. At that moment, the interviewer’s suspicion is confirmed, and often the liar’s composure breaks – they must scramble to adjust their story or confess. By contrast, if the evidence had been revealed upfront (“We have video of you there, explain it”), a clever liar might quickly concoct an explanation consistent with being seen at the scene (robbing the investigators of a chance to catch a lie). The SUE technique systematically exploits truth-default: it lets the liar hang themselves with an initial lie while the interviewer feigns trust, then uses evidence to trigger and verify the deception. This method has been incorporated into many law enforcement interview training programs. It requires discipline on the interviewer’s part to resist immediately challenging every suspect statement; instead, the interviewer plays along until the optimal moment to reveal what they know. When done correctly, guilty suspects display more contradictions and inconsistency, which observers can detect at higher rates. In short, be strategic with evidence – don’t give away your hand too early. Let the subject commit to a story under the umbrella of truth-default, then use facts to collapse any lies. (Notably, this strategy also protects truthful suspects – if someone is innocent, their story will remain consistent with the evidence when it’s revealed, and the investigator can be more confident in their honesty.)
• ABC as an Antidote to Truth-Default Bias: ABC provides a practical framework that addresses each of TDT’s vulnerabilities:
• It prevents passive acceptance of information by replacing the truth-default with investigative neutrality.
• It encourages systematic evidence checks, creating opportunities to detect deception through inconsistencies or contradictions.
• It avoids over-reliance on behavioral cues, emphasizing verification over intuition.
Moreover, the ABC model supports procedural fairness it ensures that truthful individuals are not dismissed unjustly, while deceptive individuals are not given the benefit of unearned trust. It encourages a fact-driven approach that aligns with best practices in investigative interviewing, including models like PEACE and the Strategic Use of Evidence (SUE).
Additionally, training emphasizes that nonverbal cues are unreliable officers learn not to depend on gut feelings about demeanor (which are subject to bias and error), but to focus on the content. Modern practitioner guides often echo Levine’s findings: there is no “Pinocchio’s nose” behavioral clue that universally signals deception, so overconfidence in reading body language can mislead officers. Instead, officers are taught techniques like ABC – ask more, verify more, and be patient in drawing conclusions. The front-line investigator’s job is increasingly seen as information collection rather than instantaneous lie-spotting. By adopting this mindset, investigators acknowledge their truth-default and work around it: they collect everything (assuming itcould be true or false), then rely on evidence and analysis to determine truthfulness after the interview.
• Post-Interview Verification and Analysis: Finally, overcoming TDT’s limitations continues even after the interview is over. Recognizing that many lies slip past in real time, investigators should rigorously review interview recordings, transcripts, and compare statements against known facts. This post hoc analysis can reveal inconsistencies that weren’t obvious in the moment. For instance, a suspect might confidently provide a timeline during the interview that later analysis shows conflicts with phone GPS data. Because the truth-default state during the conversation might have prevented immediate doubt, it’s crucial to double-check later with a fresh, critical eye. Some law enforcement units adopt a team approach: one officer conducts the interview (establishing rapport and gathering details, somewhat in truth-default mode), while another officer or analyst who was not in the room reviews the statements against evidence afterwards. The second reviewer has the advantage of not being socially engaged with the suspect (thus perhaps less susceptible to interpersonal trust or distraction) and can more objectively spot lies. This two-stage approach acknowledges TDT – it’s hard to both be a supportive interviewer and a lie detector at the same time. By separating the roles (at least in time, if not by person), agencies improve deception detection. Additionally, tools like statement analysis software or even emerging artificial intelligence systems are being tested to flag verbal indicators of inconsistency or deception in transcripts. While such tools are not foolproof, they assist humans in overcoming natural truth-bias by systematically examining what was said. In essence, the strategy is: don’t solely trust your on-the-spot judgment; verify and analyze later when you’re out of the truth-default influence of face-to-face interaction.
