Case File 237 · Investigation Psychology

What Is Omission, and Is Leaving Something Out the Same as Lying?

By Murder Book Editorial TeamPublished by Gungrounds, the studio making Murder BookPublished 3 October 2026Updated 3 October 2026

Omission means leaving something out — withholding information rather than stating something false. Whether that counts as "lying" depends on who you ask. Many philosophers hold that a lie requires an actual false statement, so a pure "lie of omission" is not, strictly, a lie. But most agree that deceiving someone by deliberately leaving out important information is still deception, even without a false word. Psychologists studying lies draw a similar line between concealing (leaving true information out) and falsifying (asserting something untrue). The practical point for anyone weighing a conversation is that an omission can be completely innocent — forgetting, not thinking something relevant, or keeping a private matter private — so leaving something out is not, by itself, evidence that a person is dishonest.

Key takeaways

Omission is withholding information; it differs from stating something false.
In philosophy, a strict lie needs a false statement, so a pure "lie of omission" is usually not classed as a lie — but deceiving by omission still counts as deception.
Psychologists distinguish concealment (leaving out) from falsification (asserting a falsehood); they are different techniques, often with the same aim.
Many omissions are innocent: forgetting, judging something irrelevant, protecting privacy, or simply not being asked.
Leaving something out is not proof of deceit, and behaviour cannot reliably reveal when an omission is deliberate.

Is leaving something out the same as lying?

Not automatically. The cleanest way to see this is to separate two ideas that everyday language blurs: lying and deceiving.

The Stanford Encyclopedia of Philosophy's entry on the definition of lying and deception explains that most philosophical definitions include a "statement condition" — to lie, you have to actually state something you believe is false. On that view, "so-called 'lies of omission' ... are not lies," because no false statement is made. Deceiving is treated differently: deception is an achievement, something you succeed in doing to another person's beliefs, and it can be accomplished by concealing information as well as by asserting falsehoods. In short, you can deceive by omission even if, strictly speaking, you have not lied.

This is not mere word-play. It is why a person can say "I didn't lie — every word I said was true" and still have misled someone by leaving out what mattered. For the mirror image, where something false is asserted, see omission vs fabrication.

What actually counts as an omission?

An omission is a gap between what someone knows and what they say. It ranges from the trivial to the serious:

Not mentioning something. Describing your day without mentioning the one part you would rather forget.
Answering only what was literally asked. Giving a technically complete reply that leaves out context you know is relevant.
Staying quiet. Choosing not to volunteer information at all.

The key feature is that an omission need not involve any false statement. That is what makes it slippery to judge. A reply can be entirely accurate and still incomplete, and the listener cannot see the gap directly.

What do psychologists say about leaving things out?

Deception researchers use a very similar split. Paul Ekman describes two major forms of lying: concealment, where "the liar withholds some information without actually saying anything untrue", and falsification, where the liar "present[s] false information as if it were true". Concealment is the psychological cousin of omission. Ekman notes that people often find concealment easier and feel less guilt about it than outright falsification, partly because no false words are spoken.

Steven McCornack's Information Manipulation Theory (1992) places omission at the centre of everyday deception. Drawing on the philosopher Paul Grice's conversational maxims, the theory treats the quantity of information shared as one lever people manipulate: giving less than the situation calls for is one of the commonest ways people mislead. A striking implication is that much deceptive communication is built from true statements that simply leave the misleading gaps in place. That is precisely why detecting it is so hard — there is no false claim to catch.

Can you tell a deliberate omission from behaviour?

No, and this is the most important limit. By definition an omission is something that is not said, so there is no statement to examine and no reliable "tell" to watch for. People sometimes assume a hesitation, a vague answer or a change of subject reveals a hidden omission, but the research does not support that leap. The 2003 meta-analysis of deception cues by Bella DePaulo and colleagues found behavioural signs of lying to be weak and inconsistent, and the 2006 meta-analysis by Charles Bond and Bella DePaulo found observers judge lies and truths correctly only about 54% of the time.

There is also an innocent explanation that is easy to forget: people genuinely do not report everything they know, because memory is selective and because we constantly judge what is "relevant". A gap can reflect forgetting or editing rather than concealment. What is selective memory explores how normal memory leaves things out without any intent to deceive, and why people avoid answering a question covers the many reasons someone withholds without lying.

Question	Short answer
Is a pure omission a lie?	Usually not, under definitions that require a false statement
Can you deceive by omission?	Yes — deception does not require a false statement
Is every omission deceptive?	No — many are forgetful, private, or simply not asked for
Can behaviour reveal a hidden omission?	Not reliably; cues to deception are weak

When does an omission actually matter?

Context decides. In ordinary conversation, leaving things out is normal and often polite. An omission takes on weight when there is a duty or reasonable expectation to disclose — for example, when someone is specifically asked a direct question, or when the missing information would change how a listener acts. Even then, whether a particular omission is wrongful is a question of context and, in formal settings, of rules that are beyond the scope of a psychology explainer. The safe general principle is that significance comes from the situation and the expectation to disclose, not from the mere fact that something was left unsaid.

For an interviewer, the practical move is the same as with any gap: ask directly and specifically. An omission often disappears the moment a clear, pointed question is asked — and if it does not, the useful next step is to look for independent evidence, not to treat the silence as a verdict. See why investigators ask for verifiable details for how checkable specifics help more than reading behaviour.

How does omission fit into Murder Book?

Murder Book: The Art of Interrogation is an upcoming narrative interrogation game from Gungrounds, an independent studio in Zagreb, Croatia. Its press kit names Narrative Gaps among the things players examine, alongside Fabrication, Avoidance and Emotional Leakage — and a narrative gap is, in effect, an omission: the part of a story that is missing. The game is built around conversation and observation, with cases designed for focused 5–10-minute sessions.

The research on this page is why those gaps are meant to prompt questions rather than conclusions. A missing detail might point to concealment, but it might equally be forgetting, privacy, or a detail the suspect never thought to mention. In Murder Book, a gap is a reason to ask again and to check the account against the evidence, not proof of guilt. The game is in development for PC (Steam) and mobile, with release currently planned for the end of Q2 2027. For the broader question, see can you actually tell when someone is lying.