To know how to tell when someone is lying, it helps to first look at the three basic types of lies. These are lies of omission, commission, and embellishment. What follows is a short description/definition of each, and some ways to detect each kind of lying.

Lying By Omission

A lie of omission is when a person fails to include the relevant facts that the listener reasonably expects to be included in an answer. For example, a woman says to her boyfriend, "I thought you went to the show, not to the bar." He answers, "I did go to the show. Here are the ticket stubs," but he leaves out the fact that he went to the bar after the show.

The simplest way to catch this kind of lying is to ask the most relevant questions directly. In the above example, the woman could ask, "Did you go to the bar at all tonight?" Many people are willing to avoid the truth, but not willing to lie outright, at least not in every case. Force them to make a choice and they may just tell the truth.

Lying By Embellishment

Lying by embellishment means exaggerating or changing the details. For example, a woman says, "I spent eight hours working on that project," when she wasn't actually working for most of that time. It includes exaggerating one's role in something, as when a man says, "Andy and I have this great little business," when in fact he is just an employee.

If you suspect this type of lying, the first thing to do is to get specific. Using the examples above, you might ask, "What exactly did you do for those eight hours?" or in the second case, "Do you actually own the business?" Of course, you can also go to other people or get other information to verify or contradict what was said.

Lying By Commission

A lie by commission is an entirely false statement. For example, a child says, "I didn't break the car window," even though he did. It can also involve transferring blame to others; "Andy must have broken it." It may also include improperly taking credit, as when a man says, "Do you like my idea?" about an idea that wasn't his.

By its nature, lying of this kind is harder to detect, because the speaker is obviously willing to lie outright. He may even be good at telling lies, depending on how much practice he has had. There are many "indicators" to watch for, though, and other ways to tell when someone is lying, including dozens of traps that can catch lying of this sort.

Some of the classic indicators of lying have to do with the eyes. "Shifty eyes, or the speaker looking away from you are thought to mean he is lying. Some will tell you these are myths that have been debunked by science. Neither moving the eyes nor avoiding eye contact indicates that what the person is saying is more likely to be a lie, the research shows. But the research is flawed. It relies on laboratory settings in which people are instructed to lie, and looks for universal indicators, rather than those specific to the individual.

Aldert Vrij of the University of Portsmouth in England, sought to correct this deficiency in the research by looking at real-life police interrogation videos. His idea on how to tell when someone is lying was to concentrate on cases where the true facts were later determined. He found that there were fairly reliable clues to whether a person is lying, but that these are individual, not universal.

For example, one woman might consistently avert her gaze when lying, while another might have greater eye-contact when lying. Most research wasn't testing for these individual factors, so the results seem to indicate that lie-detecting wasn't viable. But we CAN take into account individual habits and patterns of behavior.

Use what you know or can determine about the individual. Does he normally avoid eye contact? Have you seen him do this before when he was lying? Of course, avoiding eye contact or moving one's eyes could be a general sign of guilt, so be careful before assuming that it means a dishonest response to a particular question. The person may just feel guilty about something related. In other words, to tell if someone is lying, start by learning a little about the person.