Jean-Paul Sartres conception of existentialist philosophy focused upon the radical freedom that faces every human being. In the absence of any fixed human nature or absolute, external standards, we must all become responsible for whatever choices we make. Sartre recognized, however, that such freedom was too much for people to always handle. A common response, he argued, was to use their freedom to deny the existence of freedom a tactic he called Bad Faith (mauvaise foi).
When Sartre used the phrase bad faith, it was to refer to any sort of self-deception which denied the existence of human freedom. According to Sartre, bad faith occurs when someone tries to rationalize our existence or actions through religion, science, or some other belief system which imposes meaning or coherence on human existence.
Bad faith in an attempt to avoid the angst which accompanies the realization that our existence has no coherence except for what we ourselves create. Thus, bad faith comes from within us and is itself a choice a way that a person uses their freedom in order to avoid dealing with the consequences of that freedom because of the radial responsibility that those consequences entail.
To explain how bad faith operates Sartre wrote in Being and Nothingness about a woman who is faced with the choice of whether to go out on a date with an amorous suitor. In considering this choice, the woman knows that she will face more choices later on because she is quite aware of the mans intentions and desires.
The need for choices is then heightened when, later, the man puts his hand on hers and caresses it. She can leave her hand there and thereby encourage further advances, knowing full well where they might lead. On the other hand, she can take her hand away, discouraging his advances and perhaps discouraging him from ever asking her out again. Both choices entail consequences which she must take responsibility for.
In some cases, however, a person will try to avoid taking responsibility by trying to avoid making conscious choices altogether. The woman might treat her hand as merely an object, rather than an extension of her will, and pretend that there is no choice in leaving it. Perhaps she cites uncontrollable passion on her part, perhaps she cites the presence of peer pressure that forces her to comply, or perhaps she merely pretends not to notice the mans actions. Whatever the case, she acts as though she is not making any choices and hence has no responsibility for the consequences. That, according to Sartre, means acting and living in bad faith.

