"Our knowing consciousness subdivides itself into Subject and Object and contains nothing else. To be Object for the Subject, and to be our representation, are the same thing. All our representations stand towards one another in a regulated connection, which may be determined a priori, and on account of which nothing existing separately and independently--nothing single or detached--can become an Object for us. It is this connection which is expressed by the Principle of Sufficient Reason in its generality."-Schopenhauer
Leibniz offered the strict formulation of the principle of sufficient reason (PSR) as, "nihil existere nisi cujus reddi possit ratio existentiae sufficiens" ("nothing exists whose sufficient reason for existence cannot be rendered"). In other places, Leibniz offered the PSR as something like the slogan of Rationalism: "Ratio est in Natura..." (Rationalism is in nature?!). If that statement makes you cringe or become worried, you're not alone. The transition from early to later modern philosophy can itself be seen as a splintered reaction to the PSR.
While Leibniz was the first to state the PSR as if it was always a formal principle of philosophy, Hume was the first to criticize it as such. Hume argued that the PSR implies that it's a contradiction to conceive of any object of our experience without attributing to it a cause, when in fact we distinctly encounter and imagine objects without an associated cause all the time, and don't face a contradiction.
By the end of the 19th century, Nietzsche declared philosophy was firmly in nihilism, which he defined precisely as the loss of belief in the PSR, so that we no longer see any purposeful order behind the flux of the world, lose our own sense of connection and harmony with the whole of nature, and finally even doubt the reality of our world in any metaphysical sense. Half a century later, Heidegger would try to draw us out of nihilism and back into the light of the PSR, but now critical of the sufficiency of the PSR in giving us the complete understanding of reality, which to some extent must always be concealed to reason.
At the cusp of this modern reaction is Kant, whose criticism of the PSR is not a rejection of it but a setting of limits on it. Kant didn't think that the existence of anything is a distinguishing quality that informs our understanding of it, let alone that it entails a sufficient reason for the thing's existence. But he did think that anything which is an object of possible experience entails the PSR. His "Second Analogy of Experience" in Critique of Pure Reason implicitly argues for the PSR in proving that any objects of our experience in time must have a cause.
Schopenhauer's doctoral dissertation, which we will be discussing, basically outlines explicitly what the "Second Analogy" entails for the PSR implicitly. To Schopenhauer, that anything becomes an object for us is the basis for its having a reason, and there are four kinds of objects which have their own kinds of reasons for them:
- Material things
- Abstract concepts
- Mathematical and Geometrical constructions
- Psychologically-Motivating forces
Interestingly, the reasons for these objects run parallel to each other but they cannot be intermixed.
Reading for this meet is highly recommended but not required, since I will try to give Schopenhauer's arguments in their general form. I hope that working through them will resolve some of the deadlock as we read Spinoza and Leibniz at other meets.
The book is in the public domain: On the Fourfold Roots of the Principle of Sufficient Reason