Sufficient reason
from 1686 Leibniz; the name and the systematic use are his
Nothing is the case without a reason why it is so rather than otherwise — applied as a demand rather than asserted as a truth.
- Active
- from 1686
- Where
- Hanover
- Also
- principium rationis sufficientis
- Status
- In use
- Tradition
- Devices and constraints
What it is
The principle of sufficient reason holds that for everything that is the case there is a reason why it is so and not otherwise. Leibniz treats it as one of the two great principles of reasoning, alongside non-contradiction.
As a device it is a demand rather than a doctrine. Confronted with a figure, a rule or an arrangement, you ask what the sufficient reason for it being this rather than something else is — and the interesting result is usually that there is none.
How it works
Take the thing as it is. Ask why it is this rather than any of the alternatives. Distinguish a reason from a cause and from a history: that a figure has been carried forward for ten years explains how it got here, not why it is right. Follow the answers until they stop. Note where they stopped.
The demand is easy to make and very hard to satisfy, which is what makes it useful.
How it is applied
- The thing is thus rather than otherwise
- Ask what the sufficient reason for that is
- Distinguish a reason from a cause or a history
- Follow the reasons until they terminate
- Note what has no sufficient reason
The device applied
Proposition The contingency has no reason for being fifteen per cent.
- The capital budget carries a fifteen per cent contingency on every project.
- Asked why fifteen, the answer is that this is the figure the finance policy specifies.
- Asked why the policy specifies fifteen, the answer is that it was set in the 2016 review.
- Asked what the 2016 review based it on, the papers show it was carried across from the previous policy, which the archive shows adopted it from a neighbouring council's document in 2009.
- At no point in that chain does a reason appear for fifteen rather than eight or twenty-five. There is a complete causal history and no sufficient reason at all.
Therefore The figure has a history and not a reason, which matters because it is being applied identically to a road resheet with a known unit rate and to a heritage restoration where the scope cannot be known until the building is opened up.
The device found nothing wrong with fifteen per cent. What it found is that nobody can say why it is fifteen, which is enough to justify asking whether one number should govern two projects with entirely different risk profiles.
What it is good for
Inherited figures, rules and arrangements — the ones everybody follows and nobody chose. The question is trivially easy to ask and frequently has no answer.
Where it fails
As a metaphysical principle it is in serious trouble. If everything has a sufficient reason then the totality of facts has one, and that reason must either be outside the totality or necessary — which appears to make every fact necessary and eliminate contingency altogether. Van Inwagen's version of this argument is the standard modern objection and it has not been answered to general satisfaction.
Quantum mechanics presses it empirically: individual radioactive decays appear to have no sufficient reason for occurring when they do.
And as a practical demand it can be pressed past its use. Everything terminates somewhere, and treating the terminus as a defect turns the device into a regress rather than an audit.
Common misconceptions
That it demands a cause. Leibniz means a reason — an answer to why this rather than that — and mathematical and logical facts have reasons without having causes.
Where it came from
Leibniz, who names it and makes it one of the two principles on which all reasoning rests. Spinoza uses an equivalent principle throughout the Ethics without naming it.
What became of it
Abandoned as a universal metaphysical principle by most philosophers after Kant, revived in restricted forms, and thriving as a practical demand.
Lasting influence
It drives Leibniz's whole system, the cosmological argument in its modern form, and Schopenhauer's first book, which is entirely about it.
Why it still matters
Dubious as metaphysics, excellent as an audit question.
Put another way
Asking why the fence is here, and finding out only when it was built.
Texts
Gottfried Wilhelm Leibniz, Monadology
Sections 31 to 32 state the two great principles in a few lines.
Where to start
Take any standing figure in your own work and ask why that number. Follow it back. Most do not survive four steps.
The surprising bit
A principle that may be false about the universe is one of the most productive questions you can ask about a budget.
In their own words
No fact can be real or existing and no proposition true without a sufficient reason why it should be thus and not otherwise
Who held it
Peter van Inwagen
Connections
- Relies on
- The infinite regress
- Parallel to
- Grounding
The verdict
Probably not true of everything, and worth asking about anything.