Logic and Language
What this domain tests
The functions of language, the use–mention distinction, ambiguity, vagueness and definition - the tools for explaining why an argument's wording, rather than its logic, breaks down.
Functions of language
- Informative: conveys truth claims.
- Expressive: evinces feeling ("Alas!").
- Directive: guides action ("Close the door").
- Performative/ceremonial: does something in being uttered ("I apologise"). Most discourse mixes functions; logic isolates the informative use.
Use and mention
To use a word is to talk about its object (Bengaluru is a city). To mention it is to talk about the word ("Bengaluru" has nine letters). Quotation marks mark mention, and confusing the two produces category mistakes.
Ambiguity and vagueness
Lexical ambiguity - one word, several senses ("bank"). Structural ambiguity - grammar allows two readings ("old men and women"). Vagueness - no sharp boundary ("tall"). Ambiguity offers discrete alternatives; vagueness is a matter of degree.
Definitions
Stipulative (assigns a new meaning), lexical (reports established usage), persuasive (embeds a value judgement), theoretical (embeds a theory). Definitions are extensional (list the members) or intensional (give defining attributes).
Worked example
"Man is the measure of all things." "Man" may mean the individual human, the human species, or humanity collectively; the claim shifts with each reading. Naming the ambiguity, and showing how the truth value changes, is what earns the marks - not picking a favourite reading.
Traps that cost marks
Treating vagueness as ambiguity; quoting a word and then arguing about the object it names; accepting a persuasive definition as though it were neutral.