What is Principle of Sufficient Reason in Philosophy?
Science
In Leibniz-Clarke Correspondence, Leibniz introduced the Principle of Sufficient Reason (PSR) in his second letter: nothing happens without a reason why it should be so, rather than otherwise. In other words, there is a reason why everything is as it is and not otherwise. Clarke and Leibniz both endorse the PSR, but they have different interpretations on the scope of things that must have a reason.
Clarke acknowledges the PSR, but he adds that sometimes this sufficient reason, may be the mere will of God. In other words, not all wills must have reasons; the mere will of God is not in the scope of things which must have reasons to explain them. Will is the faculty of acting, or choosing. For God’s mere choice (or action), no reason is required to explain why God makes such a choice (or acts in this way) rather than otherwise. For example, if all places are absolutely indifferent to all matter, why is this particular system of matter created in one particular place rather than another (indifferent) place?
To explain this, Clarke says it could be because of the mere will of God; no further reason is required to justify such mere will!
Furthermore, for Clarke, God is the governor of the world; acting upon all things, himself acted upon by nothing. If a reason is required for God’s mere will, meaning that God cannot act without a predetermined cause, this would deny all his power of choosing. It also introduces fatality (because if all wills must have reasons, things can only happen in certain ways). Therefore, Clarke thinks not all wills must have a reason, and the mere will of God is itself a sufficient reason in Clarke’s version of the PSR.
Leibniz thinks that Clarke does not fully perceive the strength of the PSR. For Leibniz, all contingent truths are in the scope of things which must have reasons. There must be reasons to explain why these truths are as they are and not otherwise (false). By contingent truths it refers to all propositions that are true but could have been false (e.g. “I like philosophy” is a contingent truth but “1+1=2” is not). It follows that all choices must be founded on some reasons. For example, there must be a reason to explain why “I choose philosophy” is true rather than false.
Since will is the faculty of choosing, Leibniz’s version of the PSR implies that all wills must have reasons, even for God’s will. Leibniz thinks there is no such thing as a mere will, because if a mere will without any motive is allowed, it contradicts the fact that all wills must be founded on reasons. Therefore, God cannot will something, without any sufficient reason for his will. Also, if God’s actions can be based on his mere will, it contradicts God’s perfection.
There can be errors in God’s actions or choices when there is no reason involved. God’s perfection requires that all his actions should be agreeable to his reason, so we cannot say that he has acted without reason, or even that he’d prefer a weaker reason over a stronger one. For Leibniz, God, the perfectly rational being, is never determined by external things, but always by what is in himself. God knows things in the world, because he produces them continuously. Therefore, God’s own knowledge of things, before anything exists without himself, is the internal reason to explain God’s will.
Back to the example of the indifferent things, Clarke says God’s mere will can be the reason he chooses between these two (indifferent) things. In Leibniz’s interpretation of the PSR, Leibniz argues that there are no such indifferent things. Since choices must become founded on some reasons. Thus, if two things are absolutely indifferent, there is no foundation of choices, and consequently nor wills.
Moreover, for the sake of showing the instinctual interpretations between Clarke’s and Leibniz’s versions of the PSR, suppose we do have two indifferent things in the world, how does God decide to choose one thing rather than the other? Clarke would say that there could be no other reason but the mere will of God. On the contrary, Leibniz would say that there must be a reason to explain God’s choice, or will.
Clarke thinks Leibniz’s version of the PSR undermines human freedom. To Clarke, Leibniz’s version of the PSR implies necessity (there must be reasons for all wills) and fatality (once you have a reason, you can only have a certain outcome). Clarke thinks the essence of human freedom (or free will) is the power to act without the
constraint of necessity. However, in Leibniz’s version of the PSR, reason is the universal necessity for all wills. Clarke thinks such a constraint for wills denies the active power for humans to act. To him, humans have the power to act without reason as the necessary constraint, because humans are free agents. Free agents have the power to move themselves, instead of merely passive and acted upon by something.
Agents have the active power to act, but non-agents do not. For example, balance is not an agent. It can only be purely passive and become acted upon by weight. So when the two weights are equal, there is nothing to move it.
The balance itself does not have the power to act, so it stays in equilibrium, unless moved by an external motive (another weight acting upon it). On the contrary, humans are agents who have the active power to move. When there are two perfectly equal reasonable ways of acting, and no reason to determine why one particular way of acting is better than the other, humans can act by virtue of the self-motive principle, meaning that they can have the freedom to choose by themselves (without a reason). However, Leibniz’s version of the PSR says that reason is necessary for all human actions. They can only act passively. This means that humans can only act like a balance, which takes away all active power for humans to act as a free agent. And therefore Clarke says that it undermines human freedom.
Leibniz responds to this criticism by saying that Clarke does not understand the true essence of human freedom.
Humans are rational agents. Free will is about how humans, as intellectual beings, choose what they think is the best based on their reasons. In other words, free will is about performing what the human mind (the agent’s intellect) judges to be the greatest good. Humans are not less free in that account. If they want to act for their best. As a result, such an action must become founded on reasons, to explain why it is the greatest good. Reason is not constraint, but the necessary thing for humans to make the best actions. For humans to have freedom, it is not to become hindered from acting in the best manner.
Freedom, for humans, is to make rational decisions, which must be based on reasons. Without reasons, a choice would be a blind chance. For example, squirrels are animals that have will, but they are not rational.
They gather nuts in the backyard, but squirrels do it by their instincts; they don’t gather nuts because they have a reason. But for humans, since God created us as intellectual beings, our free will is based on reasons, and we would say “I choose to gather nuts, because it is the best way to save food for the winter”. Regarding freedom, humans as rational agents are always based on reasons. I think Leibniz’s version of the PSR best comports with the notion that humans have freedom. Leibniz’s version of the PSR is more convincing to me! All contingent truths must have reasons, which implies that all wills must become founded on reasons. I do not believe in Clarke’s concept of mere wills (wills that are independent of reasons).
Even though a man may think that he has his own power of choosing without reasons: “I choose to eat pizza today because I simply feel like it. My choice is based on my mere will. There is no other reason affecting me”, but truly, his action is based on reason; humans sometimes are just unaware that their reason is actually affecting their decisions.
Regarding freedom, humans do not only act based on external reasons that seem to affect them now, but they also act on the basis of their own past experiences. (For example, the man may decide to eat pizza today since, at some point in the past, he has already justified the decision by the fact that eating pizza is less time-consuming than pasta.) This process occurs unconsciously and at the level of automatism, in other words, not realized by the individual. However, it still implies reliance on reasons.
Therefore, humans cannot act without any reason at all, even if they think they possibly can. Wills is the faculty of acting. All wills must have reasons, and there is no such thing as the mere will of humans, or to have their own power of acting without reasoning. Free will can only become understood as the decisions based on reasons, but not decisions based on mere wills. Leibniz’s version of the PSR best comports with this notion of freedom which is based on human reasoning.
