“First find out who you want to be, then do what you have to do.” Epictetus
Existentialists are known for being in some regards moral skeptics through denying a conception of human nature or excellence. Sartre is perhaps the definitive example of this both in the particulars of his Existentialism and in his famous declaration which has been called the central mantra of Existentialism: Existence precedes essence. He believes that although the Enlightenment dismissed rational grounding in belief in God they hold on to what certainty in God gave them. Sartre however dismisses this “universal nature,” and this is what is meant by “existence precedes essence.” This is arguably a false claim but regardless of its truth it is not a worthwhile one. That is regardless of whether or not Man has a universal “essence” there is nothing in the description of this essence described by the Stoics, Schopenhauer or various religions (something made in the image of God) that in any way grounds what Man or any one man ought to do. That is, Sartre believes by denying an essence through denying God he is giving man the “freedom to choose” that grounds Existentialism. However, there are several unnecessary premises there and good philosophy in my mind is akin to a good steak – there should be very little fat.
First off, a God or creator is not necessary for Man to have a universal nature, telos, or “good.” The Stoics’ ethics focus on Man being a rational being who must live “according to Nature” referring to his nature as a rational being who has various needs to live well. Arguably Aristotle’s ethics is comparable. Schopenhauer’s ethics involves us denying the “will-to-life” and seeing all sufferers in this bleak existence as brother and sisters, and through this view acting with compassion rather than with selfish intent or malice. None of these views of our “nature” necessitate a God for the idea to be communicated. Secondly, a “good” or telos is not necessarily what we ought to do. Sartre by failing to realize this seems to be left in the Ancient World and fails to understand the leaps made by moral skeptics such as David Hume. That is, just because I know Vitamin C is good for me, in no way indicates that I ought to consume Vitamin C, because I have no reason to believe that I ought to be happy or healthy. This is a moral intuition we have, but intuition is not grounds for knowledge.
In fact there are some ethicists who insist that we must act contrary to our nature. This is something that someone familiar with the Christian tradition should pick up on easily. Man is sinful and fallen for the Christian. And instead of following our base urges and inclinations, it is preferable (for one reason or another depending on the Christian tradition) to turn away from our fallen nature and towards the state of being passed this veil-of-tears and world-of-woes that is the Kingdom of God and union in Christ. This asceticism and focus on the afterlife is why Nietzsche calls Christianity, but also Buddhism and the writings of Schopenhauer “life-denying” philosophies. However just as the Christian cannot ground from the will of God why I ought to obey such a will (any selfish inducement of Heaven is not satisfactory and only removes the “moral” element of doing good for the sake of good rather than for a reward) so Nietzsche does not solve the is-ought distinction either and does not rationally ground his Will to Power. To summarize, Sartre wrongly thinks that to disprove a “telos” or descriptive account of well-being, or any other descriptive account (such as God’s will) is necessary to dismiss the possibility of a concrete morality grounded in reason. But the is-ought distinction is all that is necessary to dismiss these claims.
I agree with the existentialists insofar as it is our responsibility to make our own choices in life – no one can make our choices for us. However, I disagree that we necessarily have a responsibility to make our own life choices in the sense that I disagree that we necessarily have a moral obligation to make a choice (any choice) or refer to ourselves as “morally free.” For to say this is to claim knowledge that we ought to make a choice (any choice) in ought-claims and ought not to be in Bad Faith. Sartre and the Existentialists describe with presumed accuracy the phenomena of Bad Faith; what they fail to do is to demonstrate why I ought not to live in Bad Faith. It is inevitable that I make some implicit ought-claims merely from living my life (or killing myself – the ought claim being I ought not to be alive, or ought not to suffer which being alive allows me to do) but what is not clear is that I should make “should” claims. One can make the claim that to “take on the task” of creating a moral system or making an argument for a pre-existing one is either noble or one will live a more happy, fulfilled existence by doing so – but this is a purely descriptive account. One still has not demonstrated that one ought to be noble, happy, fulfilled etc.
Since Man is a being that must choose (this is what it means, in part, to be human) he has to choose what his ethics will be – if they will correspond with a description of human nature, utilitarian calculus, personal pleasure, the Categorical Imperative, God’s will, or any other approach he can take. He must act as if something is true even if he cannot ground it in reason. And it is my contention that as long as a claim is not contradictory any claim is as good as any other claim. This is distinct from Kant’s view, who also believes we must act as if morality is true, though we cannot ground it in pure reason. However, it is also Kant’s view that we can use logic to determine what is moral and what isn’t (lying is always wrong), once again making assumptions since we cannot know anything about metaphysics. In my future paper, I will argue why Kant is wrong in believing he can determine what is right or wrong using reason.
 In the philosophic atheism of the eighteenth century, the notion of God is suppressed, but not, for all that, the idea that essence is prior to existence; something of that idea we still find everywhere, in Diderot, in Voltaire and even in Kant. Man possesses a human nature; that “human nature,” which is the conception of human being, is found in every man; which means that each man is a particular example of a universal conception, the conception of Man.
 Dostoyevsky once wrote: 'If God does not exist, everything is permissible.' This is the starting point of existentialism.