We lie by saying: "I'm fine, thanks" when we're feeling miserable. We lie when we say: "What a beautiful baby" while inwardly noting its resemblance to an alien. And most of us have simulated anger, sadness, affection, or said: "I love you" when we don't mean it.
We tell our children to smile and look grateful for the soap-on-a-rope grandma has given them for their birthday - and perhaps we add that if they don't, Father Christmas won't come this year.
Not only do we make exceptions to the prohibition against lying, sometimes we approve of it. If a doctor tells a bereaved husband his wife died instantly in the crash, rather than the truth - that she spent her last hours in horrific pain - we applaud the doctor's compassion.
We call the lies we like "white lies", but asked to define what makes a lie white we soon get lost in qualifications and contradictions. And while traditionally we frown upon liars, I'd argue that lying is a basic human necessity.
BOOST YOUR FRIENDSHIPS
We exert our powers of deception virtually from birth. One study looked at the deceits children under the age of 1 engage in and, among many examples, found a 9-month-old faking laughter as a way of signalling that he wants to join in with others who are laughing.
Lying is as innate to us as communication - and just as important to our survival.
Most of us have, at some point, perhaps in a cab or around the canteen table, found ourselves faced with a choice between pretending to agree with a political statement in which we don't believe, or being honest and risking an unpleasant argument.
We have to deal with conflicts between our desire to be truthful and our standing in the community - and often we choose to do so by lying.
"Yes, that dress looks lovely on you." "I'm so sorry I'm busy that night." "Of course I don't mind!" White lies are sticking plasters we put over everyday social problems, they're the way we avoid hurting people's feelings.
Don't agree? Just imagine being brutally honest in all of the above situations and what would happen as a result.
YOU'LL FEEL FITTER AND HEALTHIER
Lying to others is only one part of it. There are also the lies we, sometimes unknowingly, tell ourselves. And this self-deception is essential for our health.
Take the research done into a form of laser surgery for heart disease. One study compared patients who'd had the surgery against those who'd had a fake operation. Twelve months later, most of the patients who had undergone the laser surgery were in much better shape.
They revelled in a rediscovered capacity for physical exercise. They reported that their heart pains had receded and that they were feeling healthier and fitter than they had done in years.
Yet the patients in the sham group were also rejuvenated. Despite not having had any treatment, they too felt years younger and the frequency of their angina pains declined.
In terms of effects on patients, there was no significant difference between the groups.
This is an example of the placebo effect, which has shown that if a person is given something they believe will make them feel better, then they will.
It has limits, of course. There's no evidence to suggest it can stop the growth of cancerous tumours, for instance, but if we expect to feel better, we are more likely to get better - even if this expectation is based on a lie.
LIES ARE CRUCIAL FOR RELATIONSHIPS
If you were asked for a short definition of sanity, you would probably say it had something to do with being free of illusions.
But actually it helps our romantic relationships if we see our partners through rose-tinted glasses and see our own actions - in choosing that specific partner, for example - in a flattering light.
There is good reason to think that this particular type of self-deception provided a survival or reproductive advantage and was therefore spread by natural selection.
A degree of unrealistic optimism about ourselves would have helped us survive in the treacherous ancestral environment and to confidently impress potential mates. Now we live in centrally heated houses rather than caves, but we still rely on illusions to carry us through life.
We imagine having children will make us happier even though studies suggest this is, at best, uncertain (anticipating our own happiness isn't the only reason we have children, of course, but it certainly smooths the decision).
We fall in love with a person we believe is uniquely suited to us, and this helps us stick with them for long enough to raise those children.
And - crucially - most people believe their relationships to be better than most others.
FOOL YOURSELF AND BE A GREAT SUCCESS
People who are talented self-deceivers are more likely to be successful at school or in business than those who aren't. Some economists believe countries become economically stagnant when business people are too rational and sensible.
We need over-optimistic entrepreneurs who are prepared to take irresponsible risks.
Without people who are willing to ignore the prevailing wisdom and follow their instincts, many of our biggest innovations and creative leaps forward wouldn't have happened.
Every year, thousands of people with vaulting ambitions start new companies in full awareness that the odds are against them achieving the kind of world-changing success of which they dream.
Most fail or settle for something less, but a few of those companies eventually become Apple or Starbucks or Dyson.
At every turn, it seems, life undermines any strict adherence to truth.
So whether you like it or not, you are a liar.
