Argument from Definition: When Words Settle Arguments
"Is a hotdog a sandwich?" This question sounds trivial, and it is — but the form it takes is anything but. The answer depends entirely on how you define "sandwich," which means the dispute is not really about hotdogs at all. It is a dispute about definitional authority: who gets to draw the lines, on what basis, and why it matters. The argument from definition is one of the most common moves in debate, and one of the least examined. When it works, it cuts through confusion with surgical precision. When it doesn't, it disguises contested value judgements as mere matters of vocabulary.
What the Argument Looks Like
The formal structure is deceptively simple:
- Definition premise: By definition, X is a case of Y.
- Application premise: A is a case of X.
- Conclusion: Therefore, A is a case of Y — with all the consequences that attach to being Y.
In practice: "Abortion is the taking of a human life. Taking a human life is murder. Therefore, abortion is murder." Or: "Cannabis is a drug. Drugs are harmful substances. Therefore, cannabis is harmful." The persuasive force in each case derives not from evidence or inference but from the definition itself — from the act of placing something in a category that carries pre-existing properties and implications.
This is why Douglas Walton and his colleagues treat the argument from definition as a distinct argumentation scheme, closely related to — but distinguishable from — the argument from verbal classification. Both involve placing a case under a category; the argument from definition specifically invokes a stated or agreed definition as its authority.
Stipulative vs. Descriptive Definitions
The key distinction in evaluating definitional arguments is between stipulative and descriptive definitions. A stipulative definition explicitly assigns a meaning to a term for the purposes of a particular context or discussion, without claiming that this is the "true" or natural meaning. A descriptive definition claims to capture how a word is actually used in natural language, or what a concept genuinely is.
Stipulative definitions are common in law, science, and philosophy, where precision matters and ordinary language is often ambiguous. A statute might define "vehicle" to include or exclude bicycles; a medical study might define "remission" in a specific quantitative way; a philosopher might define "knowledge" as justified true belief. These are arbitrary choices in the sense that alternatives are possible, but they are not dishonest — they are explicit precision tools. The appropriate response to a stipulative definition is not to argue that it is "wrong" but to evaluate whether it is useful and whether its implications are acceptable.
Descriptive definitions, by contrast, are empirical claims about language or about the nature of things. They can be right or wrong. When someone argues that "terrorism, by definition, requires targeting civilians," they are making a claim about how the word is and should be understood — a claim that can be challenged on grounds of ordinary usage, expert convention, or conceptual coherence.
When Definitions Settle Arguments Legitimately
In many contexts, definitional arguments do real work. Mathematics is the paradigm case: once the axioms and definitions are fixed, proofs follow by pure deduction. If you accept the definition of a prime number, you cannot coherently argue that 4 is prime. If you accept the definition of a contradiction, you cannot coherently assert both P and not-P simultaneously.
Law depends heavily on definitional arguments. The question of whether a given act constitutes "assault," "negligence," or "fraud" is a definitional question — one that the legal system resolves by appeal to statutory or case-law definitions. These are human constructions, but within a legal system, they carry binding force. The court that decides whether something fits the legal definition of "employment" is not discovering a metaphysical truth; it is applying a socially established framework that has real consequences for real people.
In technical fields, too, definitional arguments are often the cleanest resolution of apparent disputes. If two scientists disagree about whether something counts as a "planet," the disagreement may be entirely definitional — and the International Astronomical Union's reclassification of Pluto in 2006 illustrates that these definitional questions have genuine stakes.
When Definitions Beg the Question
The argument from definition goes wrong — often dramatically — when the definition being invoked is itself contested, when it is used to settle a question that the definition should not be allowed to settle, or when the definition covertly assumes what it purports to prove.
Question-begging definitions are the most common failure mode. If the definition of "marriage" is stipulated as "the union of one man and one woman," then the conclusion that same-sex unions are not marriages follows by definition — but this resolves no substantive dispute. The real argument is about what marriage should mean, and that cannot be answered by appealing to a definition that one side refuses to accept. The definition is doing the work that the argument should do.
Similarly, defining "freedom" as "the absence of government interference" makes many welfare-state policies appear to be definitional violations of freedom — but only by building a particular (negative) theory of freedom into the definition itself. If you instead define freedom as "the capacity to act on one's choices," the same policies may enhance freedom rather than restrict it. The definitional choice is already a substantive political choice.
This pattern is what philosophers call a persuasive definition — a definition that is emotionally or rhetorically loaded in a way that smuggles evaluative commitments into what appears to be a neutral lexical act. Philosopher Charles Stevenson, who coined the term, noted that persuasive definitions typically preserve the positive or negative emotional charge of a word while altering its descriptive content to favour a particular conclusion.
The "No True Scotsman" Connection
A particularly notorious variant of definitional argument is the No True Scotsman fallacy. The pattern: an initial claim is made about a category ("Scots are generous"). A counterexample is offered ("But Angus is Scottish and he's stingy"). The claim is then defended by adjusting the definition: "Well, no true Scotsman would be stingy." The definition of "true Scotsman" has been silently modified to exclude the counterexample — rendering the original claim unfalsifiable.
This move is tempting and appears in serious discourse: "Real communism has never been tried." "Genuine capitalism doesn't include crony capitalism." "True democracy would never produce that outcome." Each case, the definition is stretched to exclude inconvenient data, making the category immune to disconfirmation. An argument from definition that cannot in principle be defeated by any evidence is not providing information — it is providing insulation.
Equivocation: The Sibling Fallacy
Closely related to the misuse of definitional arguments is equivocation — the fallacy of using the same word in two different senses within a single argument. "Laws of nature are laws. Laws require a lawmaker. Therefore, nature requires a lawmaker." Here, "law" shifts meaning between the first and second premise. The argument is valid only if the term is used consistently, which it is not. Definitional arguments become equivocation when they exploit the ambiguity of natural language rather than clarifying it.
Critical Questions for Definitional Arguments
When you encounter an argument from definition, these questions should guide your evaluation:
- Is this definition stipulative or descriptive? Is it being offered as an explicit convention, or as a claim about what something "really" is?
- Is the definition agreed upon by the parties to the dispute, or is it contested? If the definition is itself disputed, the argument has not moved beyond the disputed question — it has only restated it in different words.
- Does the definition beg the question? Does it covertly assume the conclusion by building evaluative content into what appears to be neutral vocabulary?
- Is the case actually a clear instance of the defined category? Even if the definition is accepted, the application of it to the specific case may be contested.
- Are there competing definitions? Especially for politically and morally loaded terms, there are usually multiple defensible definitions. Acknowledging this is not relativism — it is precision.
Why Definitional Arguments Matter
In politics and public discourse, control over definitions is a form of power. Whoever defines "terrorism," "freedom," "family," "human life," or "democracy" shapes the terms of the debate that follows. Recognising when an argument is resting on a definitional choice — and when that choice is doing ideological work — is one of the most important critical thinking skills in civic life.
This does not mean definitions are arbitrary or that definitional arguments are always suspect. It means they should be made explicit, examined, and challenged when appropriate. The argument from definition is a legitimate tool of reasoning; the question is always whether the definition is transparent, appropriate, and agreed — or whether it is smuggling a conclusion in through the back door.
Sources & Further Reading
- Walton, Douglas N., Chris Reed, and Fabrizio Macagno. Argumentation Schemes. Cambridge University Press, 2008.
- Stevenson, Charles L. Ethics and Language. Yale University Press, 1944. (On persuasive definitions.)
- Robinson, Richard. Definition. Clarendon Press, 1950.
- Stanford Encyclopedia of Philosophy: Definitions
- Wikipedia: Persuasive definition
- Wikipedia: No true Scotsman