Burden of proof
from 50 BCE Roman law; the philosophical treatment is much later
Not who is right, but who has to show it — and what happens to the question if nobody does.
- Active
- from 50 BCE
- Where
- Rome
- Also
- onus probandi
- Status
- In use
- Tradition
- Devices and constraints
What it is
The burden of proof allocates the work of establishing a claim. Whoever carries it must produce the case; if they do not, the question resolves against them without anyone having shown the opposite.
That last part is the device's whole force and the part most often missed. Failing to discharge a burden is not a draw. It is a loss, and the party without the burden wins by doing nothing.
How it works
Identify what is being asserted, as against what is being presumed. Establish which party carries the burden — normally the one asserting, or the one departing from an existing state of affairs. Establish the standard: how much is enough. Ask what follows if the burden is not discharged.
The fourth question is the useful one and is almost never asked in ordinary argument, which is why ordinary argument goes round in circles.
How it is applied
- One party asserts, the other presumes
- The burden falls on the party asserting, or departing from the existing position
- A standard is set for what discharges it
- If the burden is not discharged, the question resolves against that party
The device applied
Proposition The builder must show the crack is not structural, not the owner that it is.
- The contract provides a defects liability period, during which the builder is obliged to rectify defects.
- The owner asserts a defect: a crack in the slab edge, visible and measured at 4mm.
- That assertion carries a burden and the owner has discharged it at the first level — the crack exists, it is within the period, and it exceeds the tolerance the contract itself specifies.
- The builder now asserts something further: that the crack is cosmetic and outside the rectification obligation. That is a departure from the position the contract establishes once a tolerance is exceeded, so the burden shifts.
- If neither party engages an engineer, the question does not sit unresolved. It resolves against the builder, because the contract's tolerance sets the presumption and the builder is the one asserting the exception.
Therefore The builder must show the crack is not structural, and the cost of finding out falls on the builder because the tolerance in the contract has already placed the presumption.
Neither party has produced any evidence about the crack's cause. The whole matter is settled by working out who would lose if nobody ever did, which is what the device is for.
What it is good for
Disputes that have stalled because both sides are demanding the other prove something. Establishing who carries the burden usually ends the stall immediately, and it costs nothing to work out.
Where it fails
The allocation is a judgement, not a fact, and it is frequently the whole dispute. Whoever gets to say which party is asserting and which is presuming has effectively decided the case, and outside a legal system with settled rules there is no authority to make that call.
It is also constantly used to avoid arguing. Declaring that the burden is on the other side is a way of declining to make a case, and since the declaration is usually contestable it produces an argument about the burden instead of about the question.
Common misconceptions
That the burden always falls on the person making a positive claim. It falls on the party departing from whatever the presumption is, and presumptions can be positive — a registered proprietor is presumed to own the land, and the challenger carries the burden despite asserting a negative.
Where it came from
Roman law, where the maxim that proof lies on the one who asserts is already settled. The philosophical treatment as a device in argument generally is largely twentieth-century.
What became of it
Fully developed within legal systems, where the rules are detailed and settled, and much looser everywhere else.
Lasting influence
It structures every legal system, the design of scientific hypothesis testing, and the standard reply to unfalsifiable claims.
Why it still matters
Constant, and the single most useful question to ask of a stalled argument.
Put another way
Not who is right, but who loses if the lights go out.
Texts
Douglas Walton, Burden of Proof, Presumption and Argumentation
The fullest treatment of the device outside a legal setting, and the clearest on how it is misused.
Where to start
Next time an argument stalls, ask what happens if neither side produces anything. The answer usually ends it.
The surprising bit
A device that decides nothing about the facts decides the outcome of a great many disputes, purely by determining who has to go first.
In their own words
Proof lies on the one who asserts, not on the one who denies
Who held it
Douglas Walton
Connections
- Influenced
- The principle of charity
- Parallel to
- Ceteris paribus
The verdict
Decisive when the allocation is settled, and merely a new argument when it is not.