“Meaning and Reference” from A W Moore (ed), Meaning and Reference (Oxford U P 1993) pp 150 – 161
If the meaning of a term is a concept, the implication is that meanings therefore are mental entities. Frege asserted that meanings were public domain, that a meaning could be the same for for more than one person, and by people at different times. Hence, meanings are identified as abstract entities, though ‘grasping’ these entities is an individual, psychological act. Putnam traces the intension/extension relationship in meanings back through medieval philosophy. He sites Carnap who “accepted the verifiability theory of meaning, the concept corresponding to a term provided a criterion for belonging to the extension.” (Putnam, p150)
Theory of meaning came to rest on two assumptions:
1) knowing the meaning of a term came is a matter of a certain psychological state
2) the meaning of a term determines its extension
Putnam rejects this outright as a false theory.
Is Meaning in the Head?
Putnam asserts that meaning is matter of conditions established by knowledge. He uses an elaborate science fiction example of the changing meaning of water over time. On an identical planet called twin earth, he suggests that everything is the same, even our own dopplegangers. However, the one difference is that water is not made of H2O, it is made of some alternative we can call XYZ. In 1590, water was the clear liquid substance found in rivers, oceans etc and between Earth and Twin Earth water could be identified as the same: x is the same liquid as y. In 1950, water on Earth is H2O and water on Twin Earth is XYZ. The relation ‘is the same as‘, which is the central logic relation, is theoretical and may require an indeterminate amount of scientific investigation. Or to make an example closer to home, (hypothetically) in Sydney people refer to Beech trees as Elm trees and Elm trees as Beech trees, and in Melbourne Beech trees are Beech trees, Elm trees are Elm trees. It follows that the Sydney-sider and the Melbourne do not have different meaning extensions to their terms because of a particular difference in their psychological states, but because of linguistic hiccup. Meanings are not in the head.
Putnam invokes a cultural and social aspect to meaning in the context of linguistics:
“We may summarise this discussion by pointing out that there are two sorts of tools in the world: there are tools like a hammer or a screw driver which can be used by one person; and there are tools like a steamship which require the co-operative activity of a number of persons to use. Words have been thought of too much on the model of the first sort of tool.” (p156)