Knowledge comes from the application of the PSR

The argument

The PSR, or the principle of sufficient reason, is the corner stone of rationalist philosophy. It is the belief that for any thing that exists there is a reason. Stated that plainly the principle can look like a truism, but its force lies in what it licenses: if nothing is simply brute, then for any fact there is something further to be said about why it holds, and the philosopher's task becomes the recovery of those reasons by reasoning rather than by observation. Having perhaps been most rigorously applied by Leibniz and Spinoza, the principle shows what that method can do when pursued systematically. When applied properly, and used with other logical tools, the PSR allows a philosopher to construct a logical proof that is disconnected from sense data. Each step is licensed by the demand that something be the case for a reason, and the reasons themselves are established by argument rather than by looking at the world. The resulting chain therefore never depends at any point on how something appeared to anyone. This is the basis of the claim about objectivity. As such, the conclusions of these proofs can be considered to be true knowledge, because there is nothing in them that could be undone by a mistaken observation or a misleading appearance. This exists in contrast to scientific knowledge, which is always in some way reliant on sense data and therefore inherits whatever fallibility the senses carry: a scientific claim is only as secure as the observations that support it, and observations can always be revised. On this account the two kinds of claim differ in status rather than merely in subject matter, and it is the rationalist route, proceeding by the principle of sufficient reason, that yields knowledge which can properly be called objective.

Premises

Counter-arguments

Critics reply that the principle of sufficient reason is a contested metaphysical assumption, not a self-evident truth: there is no non-circular proof that everything has a sufficient reason, and modern physics — genuinely indeterministic quantum events — is often taken to provide counterexamples. Empiricists argue that a priori rationalist systems like those of Leibniz and Spinoza, however internally rigorous, cannot deliver knowledge of the actual world without some contact with experience, since valid deduction only transmits truth from premises, and premises about reality must ultimately answer to observation. Far from being inferior, science's reliance on sense data is what ties it to the world; a proof 'disconnected from sense data' risks being a merely consistent system with no guarantee of matching reality. So the PSR does not straightforwardly yield objective knowledge superior to empirical inquiry.

Rejecting the premises

[Rejecting P1] The principle of sufficient reason is a disputed metaphysical assumption with no non-circular justification, and indeterministic quantum events are widely taken as counterexamples, so it cannot serve as a secure cornerstone for knowledge. [Rejecting P2] Valid deduction only transmits truth from its premises; a proof disconnected from sense data cannot establish facts about the actual world, so rationalist systems do not yield objective knowledge superior to empirical science.