Rules and Fallacies of Definition
Chapter Fifty-Six
Syllabus topic 4.2, "Traditional Définition - 'rules and fallacies'"
Pages 263 to 267 of 334
In one line
A definition must state the essential attributes, must not be circular, must be exactly as wide as the term, must be clear, and must be affirmative where it can be.
In the wording a student can write in an examination: the traditional rules of definition are five in number, and each has a corresponding fallacy. A definition must give the genus and differentia; it must not be circular; it must be commensurate with the definiendum, neither too wide nor too narrow; it must not be expressed in obscure or figurative language; and it should not be negative where an affirmative definition is possible.
Rule one: a definition must state the essential attributes
The rule. The definiens must give the genus and the differentia, that is, the attributes which make the thing what it is, and not merely attributes it happens to have.
The fallacy: definition by property or by accident.
Property, from sequence 550, follows from the essence and is not the essence. "A contract is an agreement that a court will enforce at the suit of an injured party" states a property, since enforceability at somebody's suit follows from the agreement being enforceable by law, and it tells you nothing about what makes it a contract.
Accident is worse, since it is not even always true. "A will is a document typed on legal-size paper" defines by an accident.
In law this fallacy has a particular shape. A definition that lists consequences rather than conditions breaks the rule. "A public servant is a person who can be prosecuted under the Prevention of Corruption Act" defines the class by what happens to it, and gives no way of deciding whether a given person is inside it.
Rule two: a definition must not be circular
The rule. The definiens must not contain the definiendum, nor any word that cannot be understood without it.
The fallacy: circulus in definiendo, a circular definition.
The obvious form. "A judicial proceeding is a proceeding before a judicial authority." The reader who did not know what "judicial" meant is no better off.
The concealed form is the dangerous one, because the same idea reappears in different words. "Negligence is want of due care" is circular in substance, because "due" means the care that ought to be taken, and what ought to be taken is exactly what negligence is defined against. The standard corrective, which the courts adopted, is to define the care by reference to a person: the reasonable man, or in Bolam v. Friern Hospital Management Committee, decided in 1957, the ordinary skilled practitioner. Substituting a person for the missing standard is how a circle is broken.
The pair form. Two definitions each of which uses the other. "An offence is an act punishable by law; a punishment is what is inflicted for an offence." Neither is circular alone and the pair is.
Rules and Fallacies of Definition
Rule three: a definition must be commensurate with the definiendum
The rule. The definiens must apply to everything the definiendum applies to, and to nothing else. In the vocabulary of sequence 180, the two must have the same denotation.
The test. A definition is commensurate if it is convertible: "all contracts are agreements enforceable by law" and "all agreements enforceable by law are contracts" must both be true. This is the one place in Module IV where the conversion of sequence 450 does real work, and it is the reason a proper definition is an equivalence and not a mere implication.
Two fallacies break it.
Too wide, where the definiens covers more than the definiendum. "A theft is taking another's property." That covers borrowing, taking under a claim of right, and taking with consent, and it omits the dishonest intention which does the whole work.
Too narrow, where the definiens covers less. "A document is a paper writing." That excludes an inscription on stone, a caricature and an electronic record, all of which section 2(1)(d) of the Bharatiya Sakshya Adhiniyam 2023 includes in terms, its illustrations naming a map, a metal plate, a caricature and an electronic record on a server or a smartphone.
And a definition can be both at once, which is common and easy to miss: "a tenant is a person paying rent for a house" is too wide, since a lodger pays rent, and too narrow, since land may be let without a house on it.
Rule four: a definition must not be obscure
The rule. The definiens must be clearer than the definiendum, and must not be figurative or ambiguous.
The fallacy: obscurum per obscurius, explaining the obscure by the more obscure.
The obscure form. A definition that uses harder words than the term defined has failed however accurate it is.
The figurative form. "A trust is the shadow cast by ownership." Perhaps evocative, and useless as a test.
The ambiguous form is the one that matters in law. Defining a term by a word that itself has two senses moves the problem rather than solving it. If "possession" is defined by "control", and "control" bears both a physical and a legal sense, the definition has not decided anything, and this is precisely the failure that makes a definition clause generate litigation instead of preventing it.
A caution. A statutory definition may be deliberately open, using a standard such as "reasonable", because the range of future cases cannot be foreseen. That is not obscurity; it is a choice to leave the line to be drawn case by case, and it was distinguished from vagueness at sequence 50.
Rules and Fallacies of Definition
Rule five: a definition should not be negative where it can be affirmative
The rule. State what the thing is, not what it is not.
The fallacy: a negative definition.
Why it usually fails. "A minor is a person who is not of the age of majority" is not viciously wrong, and it works only because "of the age of majority" is itself defined affirmatively somewhere. Where nothing affirmative stands behind it, a negative definition tells you almost nothing: "a non-agricultural building is a building that is not agricultural" leaves the reader exactly where they started.
The exception, and it is a real one. Some terms are negative in their nature, and a negative definition is then correct. Section 2(1)(i) of the Bharatiya Sakshya Adhiniyam 2023 defines "not proved" as the state in which a fact is neither proved nor disproved. That definition is negative twice over and it is right, because the thing being defined is precisely the absence of the other two states. The rule is a rule of preference, not a prohibition.
A worked example: testing a definition clause
Suppose an Act defines: "'Vehicle' means any conveyance used for the carriage of persons or goods, but does not include a handcart."
Rule one, essential attributes? Genus: conveyance. Differentia: used for the carriage of persons or goods. Both are essential rather than accidental. Passes.
Rule two, circular? "Conveyance" is not the same word as "vehicle" and can be understood without it, though it is close enough to be worth noticing. Passes, narrowly.
Rule three, commensurate? Test by conversion. Is every vehicle a conveyance used for carriage of persons or goods? A vehicle used only for towing carries nothing, so the definition may be too narrow. Is every such conveyance a vehicle? A stretcher is a conveyance used for the carriage of persons, so it may be too wide. The exclusion of handcarts shows the drafter noticed the width problem in one instance and dealt with it by an exception rather than by the differentia, which leaves every other instance open. Fails on both counts.
Rule four, obscure? No. Passes.
Rule five, negative? The main limb is affirmative and only the exception is negative, which is the correct structure. Passes.
What the exercise produced. Two identified defects, both in commensurateness, and both of them the kind of defect that generates litigation: a towing vehicle arguing it is outside, and a stretcher-bearer arguing he is not. The five rules found them mechanically, without any knowledge of transport law.
Rules and Fallacies of Definition
Distinctions that carry marks
| Rule | Fallacy that breaks it | Legal example of the fallacy |
|---|---|---|
| State the essential attributes | Definition by property or by accident | Defining a class by the consequences of belonging to it |
| Do not be circular | Circulus in definiendo | "Negligence is want of due care" |
| Be commensurate | Too wide; too narrow | "Theft is taking another's property"; "a document is a paper writing" |
| Be clear | Obscurum per obscurius | Defining "possession" by an ambiguous "control" |
| Prefer the affirmative | Negative definition | "A non-agricultural building is one that is not agricultural" |
| Too wide | Too narrow | |
|---|---|---|
| The definiens covers | More than the term | Less than the term |
| Test that catches it | The converse fails | The original fails |
| Effect in a statute | The Act reaches people it was not meant to | The Act misses people it was meant to reach |
What this does not mean
Circularity is not always obvious. The concealed form uses different words for the same idea, and it is the form that survives drafting.
A negative definition is not always a fallacy. Where the thing defined is itself an absence, as with "not proved", the negative form is correct. The rule states a preference.
An open-textured standard is not obscurity. A statute that says "reasonable" has chosen to leave the line to be drawn case by case, which is a decision and not a defect.
Quick revision
Five rules and five fallacies.
One: state the essential attributes, the genus and the differentia. Fallacy: definition by property or accident.
Two: do not be circular. Fallacy: circulus in definiendo, including the concealed and the paired forms.
Three: be commensurate, neither too wide nor too narrow. Test by conversion: the definition must convert.
Four: be clear, not obscure, figurative or ambiguous. Fallacy: obscurum per obscurius.
Five: prefer the affirmative. Exception where the thing defined is itself an absence, as in section 2(1)(i) of the Bharatiya Sakshya Adhiniyam 2023.
The commonest defect in a statutory definition is want of commensurateness, and the conversion test is what finds it.
Test yourself
1. State the five rules of definition with the fallacy that corresponds to each.
A definition must state the essential attributes, the genus and the differentia, and the fallacy is definition by property or by accident. It must not be circular, and the fallacy is circulus in definiendo. It must be commensurate with the definiendum, neither too wide nor too narrow. It must not be expressed in obscure, figurative or ambiguous language, and the fallacy is obscurum per obscurius. And it should be affirmative rather than negative where an affirmative definition is possible.
2. How is commensurateness tested?
By conversion. A definition is commensurate when the proposition stating it converts: if all contracts are agreements enforceable by law, then all agreements enforceable by law must be contracts. If the converse fails the definition is too wide, covering things the term does not; if the original fails it is too narrow, missing things the term does cover. A proper definition is therefore an equivalence and not merely an implication.
Rules and Fallacies of Definition
3. Give a legal example of a definition that is too wide and one that is too narrow.
Too wide: "theft is taking another's property", which covers borrowing, taking under a claim of right and taking with consent, and omits the dishonest intention that does the work. Too narrow: "a document is a paper writing", which excludes an inscription on a metal plate, a caricature and an electronic record, all of which section 2(1)(d) of the Bharatiya Sakshya Adhiniyam 2023 includes and illustrates in terms.
4. Why is "negligence is want of due care" circular, and how did the law escape the circle?
Because "due" means the care that ought to have been taken, and what ought to have been taken is precisely what a definition of negligence has to supply, so the definiens contains the definiendum in other words. The courts escaped it by substituting a person for the missing standard: the reasonable man in general, and for a professional the ordinary skilled practitioner, as Bolam v. Friern Hospital Management Committee, decided in 1957, put it. Naming a person gives a test the circle could not.
5. Is a negative definition always a fallacy?
No. The rule is one of preference: state what a thing is rather than what it is not, because a negative definition usually leaves the reader where they started. Where the thing defined is itself an absence, the negative form is correct, and section 2(1)(i) of the Bharatiya Sakshya Adhiniyam 2023 is the clean example, defining "not proved" as the state in which a fact is neither proved nor disproved.
6. Distinguish an obscure definition from one that uses an open-textured standard.
An obscure definition explains the term by words that are harder, figurative, or ambiguous, so that the reader is no better placed than before: defining "possession" by a "control" that bears both a physical and a legal sense moves the problem rather than solving it. An open-textured standard such as "reasonable" is a deliberate choice to leave the line to be drawn case by case, because the range of future situations cannot be foreseen. The first is a defect, the second a decision.
The rest of this subject
These notes are cut from the University's printed syllabus. Open the syllabus itself, or the past papers, for the same subject.