Why do men lie? To either protect their reputation or to stay out of trouble. That’s the opinion of former CIA polygraph examiner Dan Crum. In his book “Is He Lying To You?” he says there are ways you can tell if a guy’s not telling the truth.

• First, think about your boyfriend’s usual behavior. How does he act and talk when he’s relaxed? That’s his so-called “WIN,” or “what is normal” behavior. Does he clear his throat or talk with his hands? You can compare his WIN behavior to how he speaks and acts when you think he might be lying.
• Another clue to see if a guy’s lying is by watching his posture and body language. Crum says a first sign of deception is that a guy will move from being comfortable and relaxed to a more formal position. You’ll notice he’ll sit up, lean forward and uncross his legs.
• You can also find out if a man’s lying by asking the right questions. Ask him an assumptive question. If you think he’s being untruthful, turn an assumption into a question. If you think he went out for lunch yesterday with another woman, don’t ask – “Did you go out for lunch yesterday?” Instead, assume that he went to lunch and say, “Where did you end up going for lunch yesterday?” Crum says this gives a guy the chance to acknowledge some part of the truth. It also forces him to come up with more than a “yes” or “no” response. Then once he acknowledges where he was – it’s natural to ask, “Who did you go with?”
• Or, Crum says you can use a bait question if you think he’s lying. Using lunch as an example again, you could ask, “Any reason why there’s a receipt for $40 from the Cheesecake Factory in your jacket?” With this approach you’re asking about the evidence without pointing fingers, or attacking him. This makes him more likely to be honest.

Crum says these simple tactics can help you spot a lie and get your man talking truthfully to you. If you’d like to go further, Dan Crum’s book is titled “Is He Lying To You?”