Questions: Natural Kind Terms and Essential Properties

Question 1

Before the discovery of chemistry, people used 'water' to refer to the clear, drinkable liquid in rivers and rain. According to Kripke and Putnam, did they mean the same thing by 'water' as we do today?

• A. No — they associated 'water' with the description 'clear drinkable liquid,' so their word picked out a different concept
• B. Yes — 'water' referred to H₂O even then, because reference is fixed by the underlying nature of the kind, not by speakers' descriptions
• C. Partially — they meant the behavioral and phenomenal properties, while we additionally know the chemical composition
• D. Yes — but only because water and H₂O happen to be co-extensive in our world

Answer: (B)

Reference is fixed at the initial dubbing by whatever natural kind is instantiated, not by the description in speakers' heads. Pre-chemistry speakers pointed at H₂O when they said 'water,' so their term referred to H₂O even though they didn't know its chemical structure. This is Putnam's insight that meaning 'ain't in the head' — what counts is the actual nature of the thing referred to, not the internal mental state of the user. Option A describes the description theory that Kripke and Putnam are rejecting.

Question 2

On Twin Earth, XYZ fills lakes and taps — chemically different from H₂O but macroscopically indistinguishable. Twin Earthers use 'water' just as we do. According to Putnam, what is the relationship between their word and ours?

• A. They mean the same as us, since they have identical perceptual experiences with the substance
• B. Their 'water' and our 'water' have the same sense but different reference — the words are synonymous
• C. Their 'water' refers to XYZ; our 'water' refers to H₂O — the terms pick out different natural kinds despite identical surface usage
• D. They mean the same as us, since meaning is determined by functional role and behavior, not chemical composition

Answer: (C)

This is the Twin Earth thought experiment's conclusion: reference tracks the underlying nature, not the internal mental life or functional role. Although Twin Earthers' use of 'water' is behaviorally indistinguishable from ours, their term refers to XYZ and ours refers to H₂O — two different natural kinds. Options A and D represent exactly the internalist/functionalist picture that Putnam's externalism is designed to refute.

Question 3

'Water is H₂O' is a necessary truth — true in every possible world — even though it was discovered through empirical investigation rather than conceptual analysis.

• T. True
• F. False

Answer: True

This is the central example of an a posteriori necessity. 'Water' rigidly designates the natural kind whose essence is H₂O — in any possible world, water is H₂O. But we could only know this through chemistry. Kripke's key contribution is separating necessity (a metaphysical category: true in all possible worlds) from a priority (an epistemic category: knowable without experience). These can come apart, and natural kind terms are the primary source of a posteriori necessities.

Question 4

Natural kind terms like 'water' refer to what ordinary speakers stereotypically describe — the typical color, taste, and behavior — since these observable properties are what fix the reference of the term.

• T. True
• F. False

Answer: False

This is the description theory, which Kripke and Putnam explicitly reject. Reference is fixed by the actual underlying nature of the kind, discovered through an initial dubbing and scientific investigation. Speakers can use 'water' correctly without knowing it is H₂O — and being told 'water is H₂O' is genuinely informative rather than a mere definition. If stereotypical properties fixed reference, 'water is H₂O' would be a contingent discovery rather than a necessary truth.

Question 5

What is an 'a posteriori necessity,' and why does the natural kinds framework generate them?

Model answer: An a posteriori necessity is a statement that is true in all possible worlds (necessary) but can only be known through empirical investigation (a posteriori). Natural kind terms generate them because they rigidly designate kinds by their underlying essence. 'Water' picks out H₂O in every possible world, so 'water is H₂O' is metaphysically necessary — but only chemistry could reveal this, making it epistemically a posteriori.

The classical assumption — that necessity and a priority coincide — breaks down for natural kind terms. The statement 'all bachelors are unmarried' is both necessary and a priori (knowable by definition). 'Water is H₂O' is necessary (water couldn't be anything else in any possible world) but a posteriori (we needed science to find out). This distinction reshapes both philosophy of language and metaphysics by showing that essences are discovered, not stipulated.