Simone de Beauvoir: Reflections on The Ethics of Ambiguity
For many philosophers today, the question of God's existence is not even worth debating anymore. Secular thought begins with the assumption, to paraphrase Nietzsche, that 'God is dead and we killed him.' If that's true, if science and reason killed the idea of God, where do we go from here? The death of God leaves many alone in the world with no heaven and no eternal reward for dutifully following all the rules; we're forced to find our way and make sense of our existence and the apparent absurdity (pointlessness) of it all.
That is both exhilarating and terrifying. Religious ethics is geared toward obeying certain rules in this life to earn a place in the afterlife. All the suffering in this existence is just a prelude, a test, for the big reward later after death. After all, what are a few decades of suffering for an eternity of bliss? Stay the course and obey the rules and everything will work out for all eternity. That's fine, I guess, but what about those of us who do not believe in God and think this life is all there is? Where do we turn to help guide us on our way?
Beauvoir's Existential Approach to Ethics
I would suggest a good place to start is the French thinker, Simone de Beauvoir. Her book, The Ethics of Ambiguity, is an accessible introduction to the fundamentals of existential ethics. Unlike Sartre, whose prose is often hard to follow, Beauvoir does an outstanding job of explaining basic existential concepts in a way the average reader can understand.
The question at the end of the day for Beauvoir is, "What must be done, practically? Which action is good? Which is bad?"
In other words, how do we judge right or wrong behavior without religion to guide us? She tells us:
"To ask such a question [about what is good or bad] is also to fall into a naive abstraction. We don't ask the physicist, 'Which hypotheses are true?' Nor the artist, 'By what procedures does one produce a work of art whose beauty is guaranteed.' Ethics does not furnish recipes any more than do science and art. One can merely propose methods." 
Ethics as Art, not Science
This sounds like basic common sense, a cop-out even, but there's a deeper point that she's trying to convey here that is actually quite insightful. What many get wrong is the belief that you can create a unified ethical system applying to every situation, a kind of one-size-fits-all top-down instruction manual for our constant moral reference. That's not how it works in practice, Beauvoir would say, any more than there is no single, unified process for creating art.
Think about that comparison for a moment. Imagine something you consider to be a great work of art; it could be Michelangelo's David, Leonardo's Mona Lisa, Tolstoy's War and Peace, Pink Floyd's The Wall, or anything else that you define as quality art. Just about everyone reading this will interpret art differently, but most will have a conception, however vague, of what art is and, I'd argue, that definition will have something to do with your subjective concepts of beauty and the sublime.
All those subjective definitions of art we come up with eventually get thinned down to a retrospective consensus of what is good art and what is not. Even so, understand that this consensus often only forms after the fact. The aspiring artist cannot find an instruction manual to create a meaningful and lasting work of art. That's not how it works. There is no science to art. A real artist does not paint by numbers nor look at what everyone else has been done and then slavishly copy it. No. We find the idea ridiculous that there could be rigid guidelines for the creation of an enduring work of art.
Beauvoir's Existential Ethics Explained
According to Beauvoir, existential ethics is similar to art. There's no blueprint, just general principles, and those principles have to be fleshed out and tested. They only thrive in a free environment where open and candid conversation is possible. We may not get our moral commandments from heaven, but we can understand a few principles that focus on well-being, not only the well-being of the individual but that of the wider community as well.
But doing this means that we first have to take the world as it actually exists. "I think that...existentialism does not offer to the reader the consolation of an abstract evasion: existentialism proposes no evasion. On the contrary, its ethics is experienced in the truth of life, a fit then appears as the only proposition of salvation which one can address to men."  Beauvoir is preaching here a kind of humanistic ethics focused on the individual, and one that many will find familiar.
At a glance, this ethics looks like a variation of the Golden Rule, or 'do unto others what you would have them do unto you'; or, we should treat others with the kind of charity that Christ taught; or, we ought to follow a Kantian morality by treating others as ends in themselves (rather than means/tools to reach our ends).  Beauvoir is not inventing anything new, but she's rightly focusing her ethics on the most humanistic aspects of the great moral traditions.
If that seems obvious, remember that Beauvoir is talking about this applying to everyone: men, women, rich, poor, black, white, and brown. Any quick survey of the world's great religions shows us how profoundly ingrained and institutionalized are racism, misogyny, and oppressive class structures, all given divine sanction by religious authorities.
Traditional Ethical Systems are Often Anti-Humanist
Remember that the next time someone name drops Ivan Karamazov and his cry that 'if there's no God, then all things are permitted!'. Even with God and gods and the best intentions, all things have been permitted anyway, all in the name of God or some other fuzzy, abstract, greater good. Religion alone holds no default moral high ground, and to argue otherwise is to ignore the crimes committed in its name over the centuries.
If God or the Party ordered it, then individuals could in clear conscience abrogate any responsibility. The Nuremberg Defense of 'I was just following orders' did not begin after 1945. It goes back a long way, giving little men with great authority a free pass to do horrible things all in the name of some higher ideal.
Many anti-humanist traditions continue today and are so embedded in traditions that practices which obviously oppress human flourishing are still considered moral because they are part of an illustrious tradition. It's not that the world is full of bad people than it is filled with bad ideas that compel otherwise decent people to do horrible things all in the name of some collectively-imagined higher purpose.
Existential Humanism is Hard
Beauvoir thought we could do better by trading these oppressive morals for more humanistic ones untethered from obsolete traditions. A true ethics does not assume the truth of tradition just because they have been around for a long time. That just gets us into trouble by promoting unreflected behavior. What she's arguing for is an ethics by and for individuals, and one that promotes the well-being of everyone instead of a select few.
We should not accept any moral truisms without examining them critically. Because they are long-held traditions is not justification enough. That does not make something moral. Everything should be scrutinized. Thus, "...one of the concrete consequences of existentialist ethics is the rejection of all the previous justifications which might be drawn from the civilization, the age, and the culture; it is the rejection of every principle of authority. To put it positively, the precept will be to treat the other...as a freedom so that his end may be freedom." 
She later reminds us that existential ethics should not be a selfish individualism that ends up as solipsism "...since the individual is defined only by his relationship to the world and to other individuals; he exists only by transcending himself, and his freedom can be achieved only through the freedom of others." 
Individual freedom looked at this way amplifies itself by pushing outward to promote the same thing in others in what becomes a virtuous cycle of free individuals supporting the freedom of other free individuals. In other words, the individual cannot truly be free without others who are likewise free.
Beauvoir believed that all the Big Ideas up to her time had promoted ethical systems that came at the expense of individual development. She was not just talking about religion, but ideology as well. "Politics always puts forward Ideas: Nation, Empire, Union, Economy, etc. But none of these forms has value in itself; it has it only insofar as it involves concrete individuals."  Value starts with the individual and works outward and upward from there, not the other way around.
Beauvoir was taking a shot at the totalitarian ideologies of her time, communism and fascism, but she'd argue that it would apply equally to nationalism, capitalism, consumerism, and any other -ism that reduces individuals to cogs in some great machine. She tells us, "We repudiate all idealisms, mysticisms, etcetera which prefer a Form to man himself."  When our ethics comes from the top down, bad things happen, injustices are perpetuated, and the kind of humanism Beauvoir is advocating suffocates and dies.
Real Freedom is Terrifying
Instead, she is arguing for an ethics that gives meaning to individual existence in a godless world. In the conclusion, she tells us, "Is this kind of ethics individualistic or not? Yes, if one means by that it accords to the individual an absolute value and that it recognizes in him alone the power of laying the foundations of his own existence."  We're the captains of our ships in a rough and stormy sea, and we are in charge of charting our course through life. We're not mere crew members tied to the rows. We get to choose, but only if we have the courage to do so.
If we're all alone in a mindless universe, we only have each other. I thrive when you do too. Keeping this in mind undermines the critique that existentialism tends toward selfish individualism and even, at the extremes, a bleak nihilism. Nothing could be further from the truth. It's a criticism from those who need everything spelled out for them in a pre-defined system, who desperately need to believe God is going to balance all the accounts in the end.
For an existentialist like Beauvoir, we should aspire for something better, but it's an open-eyed aspiration that acknowledges the deck is stacked against our success, that failure is a possibility and death inevitable. Even so, we each should strive to carve out, if only for a little while, a better world that promotes the well-being of everyone. Is that selfish or bleak? I don't think so. But it is more honest.
 Beauvoir, Simone De. The Ethics of Ambiguity. New York, NY: Philosophical Library, 2015. 144-45.
 Ibid., 172.
 Ibid., 145.
 Ibid., 154.
 Ibid., 170.
 Ibid., 157.
 Ibid., 157.
 Ibid., 169.