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A rigid designator, in philosophy, designates the same thing in all possible worlds. The word ‘water’, for example, is a rigid designator: it actually designates water. That is, it designates water in the actual world, and (unless its meaning is changed) there is no possible situation in which it designates anything other than water. That is, it designates water in all possible worlds.
A non-rigid designator does not designate the same thing in all possible worlds. The description ‘the first woman Prime Minister of Britain’ is a non-rigid designator. It actually designates Mrs Thatcher; it designates Mrs Thatcher in the actual world. But it could have designated someone else, for someone else might have been the first woman Prime Minister of Britain. That is, there are possible worlds in which it designates someone other than Mrs Thatcher.
Saul Kripke introduced the distinction between rigid and non-rigid designators. It is important because, Kripke argues, identity statements—statements that one thing is identical with another—conjoining rigid designators are, if true, necessarily true.
The word ‘water’ is a rigid designator, it designates the same thing in all possible worlds. The term ‘H2O’ is also a rigid designator, since it too designates the same thing in all possible worlds. Further, ‘water’ and ‘H2O’ refer to the same thing: water in the actual world. So ‘water’ and ‘H2O’ refer to the same thing: water in all possible worlds. The identity statement ‘water is H2O’ is not only true, it is necessarily true. It is impossible for the statement ‘water is H2O’ to be false.
By contrast, identity statements—statements that one thing is identical with another—in which one or more non-rigid designator occurs are, if true, merely contingently true. ‘Mrs Thatcher’ is a rigid designator. But ‘the first woman Prime Minister of Britain’ is non-rigid. It does not designate the same thing in all possible worlds, for someone else might have been the first woman Prime Minister of Britain. So although the identity statement ‘Mrs Thatcher was the first woman Prime Minister of Britain’ is true, it is merely contingently true. For it is possible for someone else to be the first woman Prime Minister of Britain; it is possible for ‘Mrs Thatcher was the first woman Prime Minister of Britain’ to be false.
Kripke\'s claim that identity statements conjoining rigid designators are, if true, necessarily true is extremely important. Philosophers have long held that the distinction between the a priori and a posteriori and the necessary and contingent coincide. A statement is a priori just if it can be known to be true or false independently of experience, a posteriori just if it cannot be known to be true or false independently of experience. A statement is necessarily true just if it cannot be false, necessarily false just if it cannot be true. And a statement is contingently true just if it is true but could have been false, contingently false just if it is false but could have been true.
Philosophers, then, have long held that a statement is a posteriori just if it is contingent. But if Kripke is right, then some statements are a posteriori and necessary. Consider the identity statement ‘water is H2O’. As we have seen, this statement is not merely true but necessarily true. Further, it is a posteriori. One cannot know that water is H2O independently of experience. One can only know that water is H2O if one has an experience such as an experience of a chemical experiment or of a chemistry lesson. AJ
See also modality.Further reading S. Kripke, Naming and Necessity. |
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