Gottfried Wilhelm Leibniz

Gottfried Wilhelm Leibniz is presented as a major interlocutor in Sartre’s account of possibility and temporality: his theories expose the difficulty of grounding necessity and succession, but Sartre argues that they cannot explain how possibility belongs to real beings or how time holds together while separating its moments. Across discussions of divine understanding, Adam’s alternatives, and continuity, Leibniz’s solutions repeatedly lead back to a unity that Sartre thinks only the For-itself can sustain.

Possibility, Necessity, and Divine Thought

Leibniz’s account of necessity, which Sartre notes was later taken up by Immanuel Kant, defines the necessary through possibility: a being is necessary when its possibility implies its existence. Sartre objects that this explanation describes a passage from ignorance to knowledge, not a foundation in being. If possibility comes before existence, it does so for thought; it is external to the being whose possibility it is. Sartre’s counterexample makes the distinction concrete: a rolling billiard ball does not contain, as one of its own properties, the possibility that a fold in the cloth will divert it. That possibility is established as an external relation by a witness. In contrast, a possibility that belongs to a being as its own power cannot supply the ultimate necessity of that being. Sartre’s conclusion is that God, if he exists, is contingent.

Sartre then sets Leibniz’s account of the possible beside Spinoza’s. Spinoza treats possibilities as products of human ignorance, destined to disappear with complete knowledge. Leibniz gives possibilities a different status: they are objects of divine understanding, and the divine will realizes the best system among them. The contrast permits a statement that sounds incompatible with strict determination: Adam might not have picked the apple. For an all-knowing understanding, Adam’s decision in the actual order can be known with certainty; the alternative is possible in another system of co-possibles, in which Adam does not eat from the Tree of Knowledge.

Yet Sartre argues that this alternative has reality only as an unrealized thought in divine understanding. Leibniz’s account therefore does not escape the subjectivity it appears to overcome; it transfers possibility from finite human thought to divine thought. Sartre acknowledges Leibniz’s suggestion that possibles might organize themselves into systems of co-possibles, with the fullest and richest systems tending toward realization. But he stresses that Leibniz does not develop this doctrine. If possibilities already possess the same kind of being as actual things, they cease to be merely possible; if they are idea-forces that prompt the divine will, their efficacy remains inside thought. Either way, represented possibility loses the character of a concrete property of an existing being.

Possibility as a Power of the Real

Sartre’s alternative begins from ordinary claims about what can happen. Looking at clouds, someone says that it may rain. The possibility is neither simply ignorance about what the weather will do nor a contradiction-free item in a separate inventory of unrealized worlds. It belongs to the clouds as a transcendence toward rain: the clouds carry a possible future without guaranteeing its realization. Likewise, a friend who is expected may come; the possibility belongs to the friend as an existing being capable of coming. Rain is possible only where clouds exist to sustain that possibility. For Sartre, the unrealized state is the possibility of a particular existent, which bears both the possibility and the non-being of its future state.

This account sharpens the limit Sartre finds in Leibniz. A system of co-possibles can describe how an alternative is thinkable, but it does not explain the lived structure in which an existing being is its possibilities without yet being them. In Sartre’s analysis, the possible arises with the For-itself’s nihilation of the In-itself and its distance from itself. It is not an instrument added afterward to reunite a self with itself. The For-itself is projected toward possibilities that it has to be in the mode of not being them; this movement carries consciousness beyond the instant. Against a possibility located only in a divine representation, Sartre insists on the concrete existent whose being sustains what it may become.

Time and the Problem of Succession

Leibniz also enters Sartre’s critique of theories that try to construct time from elements that are themselves non-temporal. Sartre describes Descartes as grounding temporal unity in God’s continuous creation and Kant as grounding it in the synthetic unity of the “I think.” For Descartes, material content is maintained through perpetual creation ex nihilo; for Kant, the concepts of pure understanding apply to time’s form. Sartre’s criticism is that both explanations assign a temporal function to a supposedly extra-temporal source. If time is real, that source would have to reach moments where they occur: even God would have to wait for sugar to dissolve. If divine knowledge does not wait, then waiting and chronological order risk becoming merely the confused appearance of an eternal logical order.

In reaction to Descartes, Leibniz rejects the problem of passage from one instant to another and the proposed solution of continuous creation. Sartre reports that Leibniz instead treats time as a vast, continuous flow, without original elements existing in themselves as instants. This avoids making succession depend on a series of isolated moments, but Sartre argues that it leaves the source of continuity unexplained. Before and after do not merely connect; they also separate. If time is continuous, its cohesive power still needs an account. A continuum is a fact to be explained, not an explanation in its own right.

Continuity, Change, and Sartre’s Objection

To make the difficulty vivid, Sartre examines Henri Poincaré’s definition of a series as continuous when a equals b, b equals c, while a differs from c. The formula suggests a being that is and is not what it is: the intermediary b is indistinguishable from each endpoint, although the endpoints are distinct. Sartre grants that such an intermediary helps articulate the relation of before and after, but asks how it can exist in this divided yet unified way. Why does it not split into two terms, one resolving into a and the other into c? The unresolved question is one of unity. Sartre argues that only the For-itself can exist in this ekstatic unity, being outside itself while holding temporal relations together. In his view, Leibniz’s continuity ultimately conceals a cohesion modeled on absolute logical immanence, or identity.

The same objection shapes Sartre’s discussion of duration and change. Sartre attributes to Leibniz, as well as Kant, the argument that change presupposes permanence: without something enduring through change, there would be no change to measure. He argues that this makes temporality only the measure and order of change, and that Leibniz’s account of change as the logical development of a permanent subject’s attributes leaves no genuine temporality. The supposed unity of what changes and what remains cannot be merely external; it must be a unity of being, which means the permanent would itself have to be what changes. For Sartre, that is an ekstatic structure, not a relation between self-contained in-itself elements.

Sartre also rejects permanence as a necessary foundation for change. A prior state can persist as past, making the present change intelligible through its relation to what it was, without requiring an underlying permanent substance. Change can therefore be absolute, even a metamorphosis affecting the whole of being. Sartre invokes experiments of the Gestalt school to support the claim that changes may be imperceptible up to a threshold and then extend to the total form. Human reality especially requires such absolute change: consciousness must become what it is in the mode of having been it, as each present becomes the past of a new present. Leibniz’s appeal to permanence, in Sartre’s reading, cannot account for this lived duration; the relation to the past already does the work for which permanence was introduced.