Here is a formal presentation of Sartre’s argument for human freedom by Jeffrey Gordon in the book Just the Arguments (Wiley-Blackwell, 2011):
P1: In order for a given state of affairs deterministically to cause a human action, the causal efficacy of that state of affairs would have to derive exclusively from characteristics of that state of affairs.
P2: A given state of affairs has no meaning in itself.
P3: If a given state of affairs has no meaning in itself, its meaning must be conferred upon it by the person experiencing it.
C1: The meaning of a given state of affairs must be conferred upon it by the person experiencing it. (modus ponens, P2, P3)
P4: The meaning of the state of affairs is the source of its power to motivate (or cause) the action.
P5: If the meaning of the state of affairs is its power to motivate (or cause) the action, then in the case of human action, the causal efficacy of the state of affairs does not derive exclusively from characteristics of that state of affairs.
C2: In the case of human action, the causal efficacy of the state of affairs does not derive exclusively from characteristics of that state of affairs. (modus ponens, P4, P5)
C3: No given state of affairs can deterministically cause a human action. (modus tollens, P1, C3)
P6: If no given state of affairs can deterministically cause a human action, then one’s actions are free.
C4: Human beings are inescapably free. (modus ponens, C3, P6)
Sartre argues that the ability to give meaning to something presupposes the capacity to negate. So negation is at the root of the freedom we have. Here is an excerpt from the Internet Encyclopedia of Philosophy that gets the point across with reference to Sartre’s work Being and Nothingness (BN):
“Sartre (BN, 9-10) discusses the example of entering a café to meet Pierre and discovering his absence from his usual place. Sartre talks of this absence as ‘haunting’ the café. Importantly, this is not just a psychological state, because a ‘nothingness’ is really experienced. The nothingness in question is also not simply the result of applying a logical operator, negation, to a proposition. For it is not the same to say that there is no rhinoceros in the café, and to say that Pierre is not there. The first is a purely logical construction that reveals nothing about the world, while the second does. Sartre says it points to an objective fact. However, this objective fact is not simply given independently of human beings. Rather, it is produced by consciousness. Thus Sartre considers the phenomenon of destruction. When an earthquake brings about a landslide, it modifies the terrain. If, however, a town is thereby annihilated, the earthquake is viewed as having destroyed it. For Sartre, there is only destruction insofar as humans have identified the town as ‘fragile’. This means that it is the very negation involved in characterising something as destructible which makes destruction possible. How is such a negation possible? The answer lies in the claim that the power of negation is an intrinsic feature of the intentionality of consciousness. To further identify this power of negation, let us look at Sartre’s treatment of the phenomenon of questioning. When I question something, I posit the possibility of a negative reply. For Sartre, this means that I operate a nihilation of that which is given: the latter is thus ‘fluctuating between being and nothingness’ (BN, 23). Sartre then notes that this requires that the questioner be able to detach himself from the causal series of being. And, by nihilating the given, he detaches himself from any deterministic constraints. And Sartre says that ‘the name (…) [of] this possibility which every human being has to secret a nothingness which isolates it (…) is freedom’ (BN, 24-25). Our power to negate is thus the clue which reveals our nature as free.”
Sartre thinks meaning motivates an action because we have the capacity to attribute meaning to mere facts through negation and imagination. For example, let’s take two people from a poor neighborhood. Both people are acted upon by various physical and social aspects of their environment. But one sees these aspects as opportunities to develop various virtues – hard work, perseverance, courage, and so on. He gives meaning to the facts of the world around him through his capacity to negate the in-itself and project possibilities to become a successful person because of his economic limitations. He is a for-itself attributing meaning to the world. This meaning, internal to him and secreted by the nothingness of consciousness, is really what is driving him to be that successful man he seems himself becoming. All human action must be driven by such meaning, otherwise it would be mere motion; it would be like water flowing down a mountain, the movement of the in-itself. Likewise, the other person sees his impoverished environment as an occasion for despair and pessimism: he gives the world a very different meaning and thus never becomes successful because of his freedom.
This analysis helps us see how the argument may be invalid. After all, we now see that premise 4 already presupposes that we have the freedom to negate and therefore not be fully determined by external forces. But since freedom is the very thing to be proven, the argument may beg the question and be an instance of viciously circular reasoning.
For an argument for freedom from doubt with reference to Sartre and Descartes, go here.
For an argument for free will from critical thinking, go here.
For an argument for free will from the assertion of truth, go here.
For some notes on Sartre’s philosophy, go here.
For my application of Sartre’s ideas on racism to contemporary social justice issues, go here.