The method of cases
from 1600 The casuist tradition; the analytic form is twentieth-century
Test a proposed rule not by argument but by running it across a graded series of cases and seeing where it starts giving answers nobody will accept.
- Active
- from 1600
- Where
- Salamanca, later Oxford and Princeton
- Status
- In use
- Tradition
- Analytic tools
What it is
The method of cases takes a proposed principle and runs it across a series of situations arranged so that they differ from each other by one feature at a time. Where the principle's verdict and the considered judgement come apart, you have located something the principle is missing.
It overlaps with the thought experiment and is not the same. A thought experiment isolates one variable in a single constructed case, often an impossible one. The method of cases needs a series, and the cases are usually ones that could actually occur — the information is in the pattern of where the verdicts diverge, not in any single case.
How it works
State the principle. Build a series of cases that differ by one feature at a time, from clear to contested. Record the principle's verdict and the considered judgement on each. Find the case where they first diverge. Ask what feature changed at that point.
The last step is the payoff. The divergence point identifies the feature the principle failed to capture, which is more useful than knowing the principle is wrong.
The moves, in order
- State the principle to be tested
- Build a series of cases differing by one feature at a time
- Record the principle's verdict and the considered judgement on each
- Locate the first case where the two diverge
- Identify the feature that changed there
The procedure
Proposition The bushfire levy exemption should turn on occupancy, not on structures.
- The proposed principle is that a rural lot pays the levy if it carries an insurable structure.
- Case one: a house, occupied year-round. Principle says pay; everyone agrees.
- Case two: a house, occupied six weeks a year. Principle says pay; everyone still agrees, since the brigade would attend either way.
- Case three: a hay shed with no dwelling, on a lot nobody visits for months. Principle says pay; the panel splits, but most accept it — a shed fire still brings trucks.
- Case four: a bare lot with a stock trough and no structure at all, adjoining the state forest, where two of the last four fires started. Principle says do not pay; the panel unanimously rejects that, because this is the lot the brigade is most likely to be called to.
- The verdicts diverge between cases three and four, and the feature that changed is the presence of a structure — which turns out to be tracking insurable value rather than call-out likelihood.
Therefore The principle should turn on the likelihood of the brigade attending, not on whether a structure stands, and the case series shows exactly where the structure test stops tracking the purpose.
No single case would have shown this. Case four alone looks like an unfortunate edge; the series shows that the principle was measuring the wrong thing all along, and identifies which thing.
What it is good for
Testing any proposed rule before it is adopted. It is standard in ethics, standard in law reform, and the single most useful thing a committee can do with a draft policy.
Where it fails
It rests on the considered judgements being reliable, and experimental philosophy has found them unstable — sensitive to the order cases are presented in, to wording, to the respondent's background and mood. If the judgements shift with presentation, the divergence point shifts with them.
The series can also be built to lead somewhere. Arranging cases so that each is a small step from the last is exactly how a sorites works, and a well-constructed series can walk someone from a judgement they hold to one they would have rejected outright if shown it first.
Common misconceptions
That it is the same as the thought experiment. The thought experiment does its work in one constructed case; this needs the series, and reading a single case as decisive is the commonest misuse.
Where it came from
The casuist tradition of the sixteenth and seventeenth centuries built enormous case series for moral theology, and was so thoroughly discredited by Pascal's mockery that the word casuistry became an insult.
What became of it
Revived in the twentieth century without the name, and now the default method in applied ethics, bioethics and law reform.
Lasting influence
Thomson's series on abortion, Foot's on doing and allowing, and the whole structure of common law reasoning by graded precedent.
Why it still matters
The most practically useful method in group C.
Put another way
Walking a fence line to find where it stops holding.
Texts
Judith Jarvis Thomson, A Defense of Abortion
A masterclass in case construction, whatever the reader concludes about its subject.
Where to start
Take a policy you have to apply and build the series yourself, from clearest to hardest. The divergence point is usually a surprise.
The surprising bit
Casuistry was destroyed as a discipline by a satirist and rebuilt three centuries later by moral philosophers who avoided the word.
In their own words
The cases are not decorations on the argument; they are the argument
Who held it
Blaise Pascal, as its enemy
Connections
- Relies on
- The counterexample, The thought experiment
- Influenced
- Reflective equilibrium
- Parallel to
- Argument by analogy
The verdict
The best available test of a rule before it meets reality, resting on judgements that are less stable than the method assumes.