I recently attended a conference where the keynote speaker, a renowned academic, talked about science and conscience.
One of the slides he showed was a quote from Sophocles, the Greek "tragedian" or playwright (496-406BC), which went: "There is no witness so terrible and no accuser so powerful as conscience which dwells within us."
In most people, the conscience does play a big part in directing the way we behave.
It may come from the values our parents or teachers instilled in us, or maybe it is something inherent in us, but the conscience is that little nagging voice in us that makes us feel guilty or ashamed when we have done something we should not have.
From childhood, that voice tells us that taking something that is not ours is wrong, cheating in exams is unfair or calling people names is hurtful. It is that uncomfortable feeling when we have done one of these things and do not own up to or apologise for it.
Everyone has a conscience - some psychologists say that we are born with an innate sense of fairness that either develops or lessens, depending on what happens in our lifetimes.
In any case, people have enough of a conscience to realise that some actions are regarded as anti-social behaviour and, therefore, must be hidden from others if carried out.
Consequently, nobody openly declares that they are going to steal, cheat or do anything that common sense says we should not, especially if we want to live among other people.
Our conscience is also the nasty feeling in our stomachs when we tell a lie.
When we were kids, we knew what would happen if we were caught lying to our parents. We might tell them that we had not got our report cards yet, but it would be difficult to keep a straight face when they kept questioning us about it.
Eventually, the pressure would become too much to bear and we had to shamefacedly hand over our red mark-filled card and wait for dad's wrath.
Those memories of the consequences of lying usually stayed with us until adulthood, training our conscience on the virtues of honesty. As horrible as it may be sometimes, it is usually better to own up when we are at fault.
This assumes that the things we need to own up to are fairly innocuous things, like our age or the fact that we forgot to pay a bill on time.
But our conscience can only be burdened with so much; if we do something really terrible, then we need to stop that conscience pricking us or else we cannot sleep at night.
Thus, we start inventing justifications for the terrible things we did, or start telling ever bigger lies in order to cover up what we did.
After a while, we start to believe our own lies and even that we never did anything wrong.
I have known some consummate liars and I often wonder how they keep track of every lie they tell.
Everything depends on keeping every story unimpeachable, and making sure that nobody is able to compare stories with anyone else.
It must be a terrible strain and at some point you are bound to trip up. That is when things start to unravel.
When they do, there is a mad scramble to keep things together, which necessitates more and more lies. That conscience, that nagging voice, that inner compass that tells us where true north is, becomes muffled and ignored altogether.
Yet it has a way of peeking out and showing itself in odd ways; the inability to look anyone in the eye, a voice that is not convincing, a hand that is shaky.
They are signs that can be seen by a shrewd observer, though perhaps not by those who prefer not to.
Luckily for societies, not everyone becomes completely devoid of conscience. Otherwise, they would become totally lawless and dysfunctional.
By and large, most people still obey traffic lights because they know it is a good thing to do. And they also do get angry at people who do not.
They may tolerate the odd person running a red light but not if it becomes an epidemic because, obviously, it becomes very dangerous for everyone. It is those people who still have their conscience who will save society.
Today, when everything in our society seems to be crumbling, when our leaders have become the ones who run red lights, we have to rely on those traffic cops who have the conscience to do their jobs correctly, without fear or favour.
If we get rid of traffic cops so that we can run red lights with impunity, then we might as well be a society before there were laws regulating our behaviour on the roads.
Imagine if our conscience stopped being our red light.
The writer is a human rights activist who works on women, children and HIV/Aids issues. The views expressed here are her own.